- Welcome, everyone. "Wednesday Nite @ the Lab."
I'm Tom Zinnen and I work here
at the UW-Madison Biotechnology Center.
I also work for UW Extension Cooperative Extension,
and on behalf of those folks and our other co-organizers,
Wisconsin Public Television, Wisconsin Alumni Association
and the UW-Madison Science Alliance,
thanks again for coming to "Wednesday Nite @ the Lab."
We do this every Wednesday night fifty times a year.
Tonight it's my pleasure to introduce
to you Jean-Michel Ané.
He's a professor in agronomy here at UW-Madison.
He was born and raised in Montpelier in France,
went to undergraduate at the University of Leon in France,
and got his PhD at the University of Toulouse in France.
(laughter) Yeah.
Then, he did a post-doc at,
I think we pronounce it UC-Davis?
(laughter)
And then came to Madison in 2004.
He is just the latest in a long line
of rather extraordinary researchers
on soil microbes' interactions with plants.
So when you think of people like Robert Burress
and Ira Baldwin
and E.B. Fred,
that's kind of like the Curly Lambeau and Lombardi
and Nietzsche of the world of nitrogen fixation.
So, to let you have an idea of what Wisconsin
has meant to the world from nitrogen fixation point
of view and plant root microbe interactions,
this is pretty cool.
I'm looking forward to this.
I was born and raised as a plant pathologist,
and to get to hear about this, the symbiosis
that are both helpful and hurtful, is gonna be great.
Please join me in welcoming Jean-Michel Arne
to "Wednesday Nite @ the Lab."
(applause)
- Thank you.
It's a pleasure for me to be here
and to have the opportunity to talk about my favorite topic
which are these beneficial associations
between plants and crops in particular and microbes.
So, the way I'm gonna structure my talk,
I often use that image of a tree, as you can see,
where I talk a little bit at the beginning
about what we call symbiosis,
what we call symbiotic associations,
because that term is often the source
of some kind of misunderstanding.
And then as you can see, I'm gonna talk on the right
about what I call the problem,
which is that kind of fertilizer that we use,
and I'm gonna talk about both the UT
and the advantages of fertilizers,
but also the problems that they cause,
both in terms of sustainability of our agriculture
and in terms of development for the developing countries.
I'm gonna talk about microbes and what microbes can help,
can do to help us solving these problems.
That's the root of my tree.
I'm gonna talk in microbes in particular,
and all that, leaving the soil, and then I'm gonna talk
about the trunk, the core of what we are doing
in my lab as well as many other colleagues are doing
in the world to try to better study these associations
in order to use them.
And that's really where I'm gonna talk about what I call
the sweet talks and the trade deals.
The sweet talks, it's a way for us to refer
to the signal exchanges on how plants and microbes
recognize each other, how a plant is about
to recognize a beneficial microbe
from a pathogen, for instance.
The trade deals, it's about the nutrient exchanges.
Plants and microbes exchange nutrients
and these nutrient exchanges are highly regulated.
In particular what the plants want to do is avoid cheaters,
and I'm gonna talk about how the plant can avoid microbes
that try to get benefits from the plant
without giving it any benefit, anything else in return.
And then for the fruits of the research,
that's the application of the research.
I'm gonna talk about what we do about relatively
short-term applications, the low-hanging fruit if you want,
what we do with serving farmers, in particular,
also tomato growers in Wisconsin.
I'm gonna talk about also more long-term projects
that we are working on to try to again engineer,
improve these associations between plants and microbes,
to try to take better advantage
of the microbes in agriculture.
So first, let's start with my yin yang sign on the top
which is often the way that people have in mind
when they think about symbiosis.
They think about something which is mutually beneficial.
Well, it's almost right.
In fact what we call symbiosis,
the definition was coined by Anton de Bary in 1879,
as a prolonged living together of different organisms
that is beneficial for at least one of them.
And that may be the surprise for you because many of you
may think it has to be beneficial for both of them.
Well, the reason we say at least one of them
is that in symbiotic associations we want
to include three types of interactions.
The one that you probably had in mind,
which is the mutualistic association on the left,
which is when these relationships
are beneficial for both partners.
That's what most people think
when they think about symbiosis.
But in fact, things like commensalism,
when the association is beneficial for one and neutral
for the other partner, is also part of symbiosis,
and even more surprisingly, parasitism,
when it's beneficial for one and detrimental
for the other one, for the other partner,
it's also part of what we call symbiosis.
The reason we have such a fairly large definition
for symbiosis is that in real life, in nature,
every association is going to shift one end from the other.
Some associations are mostly mutualistic most of the time,
but some are sometimes depending in particular
on the environment or let's say even the age of the plants,
sometimes these associations are going to turn more
to the parasitic end,
and you have really nature that continuum.
Of course what we want to do as agronomists,
is to have associations that are as beneficial
for the crop and we try to shift that continuum
to where its a more mutualistic association.
So, that's what we mean when we talk about symbiosis
and so we should not be surprised if sometimes even some
of the very classical symbiotic associations that we use,
like I'm gonna talk about soy beans
and bacterial (mumbles)
can be sometimes more into a parasitism.
It's just the nature of these relationships.
Regarding plants and microbes, so that's really what we
are focusing on today, we are talking
about these relationships between plants and microbes.
What is the deal, what are the exchanges
that take place between plants and microbes.
So my pine tree symbolizes the plant,
and what plans are good at, they are good
at doing photosynthesis.
They are good at getting carbon from the atmosphere
and producing sugar, photosynthesis.
And that's really the main nutrient
that plants give to their microbes.
In addition, they also provide what we call
an ecological niche, which is simply a place
for the microbes to grow and avoid competition.
In return, microbes, and here I used the image
of my mushroom, the fungus,
is these microbes can really give everything
that a plant needs to grow.
I don't know if you all have a garden but you know
that plants need water, they need nutrients,
if you're using a can of fertilizer
you have NPK, nitrogen phosphorous potassium.
Microbes can provide water,
can help plants for the acquisition of water.
They can help plants getting their nutrients from the soil
or from the air, in same cases,
and also these microbes sometimes can help the plants
against pathogens, and that is in particular the case
of many fungi and bacteria that help protecting
their host, their plant, against pathogens.
So these are typically the deals,
the kind of exchanges that take between plants and microbes.
So before continuing, I'm gonna talk
about what I call the problem.
Why do we really care about studying
plant microbe associations.
What are the problems that we hope solving
or at least alleviating by working with plants and microbes.
In my opinion, these problems have to do
with agricultural sustainability for developed countries
like in the U.S. or in Europe or in China,
and also problems of agricultural development
in particular for developing countries.
That's what I call the growing problem.
How can we grow our crops
without destroying our environment,
or how can we grow our cops to reach
the maximum yield possible.
So, in developed countries you probably know
that we use a lot of fertilizer, and in particular,
a lot of nitrogen fertilizer.
This nitrogen fertilizer is coming from natural gas.
We use a process the Haber-Bosch process that was invented
at the beginning of the 20th century,
to use the energy coming from natural gas
to convert nitrogen from the atmosphere,
nitrogen that we call dinitrogen into ammonium.
That chemical reaction requires a lot of energy.
You need about one ton of natural gas
to produce one ton of fertilizer.
At a global scale in the world,
we use 2% of the world's energy to make fertilizers.
So, we spend a lot of energy, we use a lot of fossil fuel
to produce that fertilizer and that's a great things
because that's what use to grow our crops.
On this graph here, I'm sorry I apologize because
it's a bit complex, what I want to focus on is that line,
that black line that increases,
the dark one is the world population.
As you know currently, we have about 7 billion people
in the world.
The other line I want you to look at is that dotted line,
black dotted line, that starts about in 1920s
and that keeps increasing and that line represents
the percentage of the world population
that is fed on that Haber-Bosch process,
that is fed using chemical fertilizers.
As you can see, that started at the beginning
of the 20th century, that's when this process was invented,
but you have a really drastic increase
in the sixties, seventies.
That time is what we call the green revolution.
One key component of the green revolution
in the sixties and seventies was to intensify the use
of nitrogen fertilizers.
Currently, you see that dotted line,
it goes up to about 50%.
Currently, half of the world population
is fed using nitrogen fertilizers.
It's obviously a great thing.
Without nitrogen fertilizers,
we would not be able to feed half of the world,
so obviously nitrogen fertilizers are absolutely necessary.
So that's obviously a plus for them.
Something which is more worrying is that we make
these nitrogen fertilizers out of fossil fuel,
out of natural gas, and it's a finite resource
and we know that well, sooner or later,
we won't have so much fossil fuel available.
If you see, we are using fossil fuel to produce fertilizers
to grow half of the food of the world,
to grow also feed for animal
which is something even more ironic,
we use these fertilizers to produce bio-fuel,
to make bio-energy, so we are using fossil fuel
to produce bio-fuel.
So obviously I think it makes sense
that it's not really sustainable, so I think that's one
aspect which is obvious, so,
yes we're getting questions, should we ask questions I think
at the end, sorry.
Great.
One of the consequence of that relationship
between natural gas and fertilizers
is that the price of these nitrogen fertilizers
is highly dependent on the price of gas.
What I show you on that graph in blue what you have
is the price of natural gas.
As you can see, there was a peak in 2001
and that corresponds to a peak in the cost
of fertilizers in red.
And again, when the price of natural gas is increasing,
the cost of fertilizers is increasing.
I don't show you the graph after that,
in fact it's actually decreasing.
The price of fertilizers and the price of natural gas
are decreasing currently due to fracking
but we know that is a finite resource.
We know that sooner or later these prices
of the natural gas, the price of natural gas
is going to increase again and that is going
to drive again the price, the cost of fertilizers.
So there are economical consequences on that dependence,
relationship between natural gas and fertilizers.
Another aspect, health consequences.
As you probably know, the maximum allowed,
maximum concentration of ammonia
in drinking water is 10 ppm.
It's unsafe to consume water that has more
than 10 ppm of nitrate.
And what I show you here is the percentage of wells
in Rock County, so Wisconsin, that have levels
of nitrate above that limit of 10 ppm.
When I came here in 2004, it was about 25% of these wells.
As you can see, over the years,
now we are at about 50% of the wells.
So what happens here is that all the fertilizer
that we apply for agriculture leaches down into ground water
and contaminates that ground water,
and contaminates these wells and this is obviously a concern
so these high levels of nitrate in drinking water
are just directly the consequence of our intensive use
of nitrogen fertilizers.
Well, that nitrate doesn't end up just in ground water.
It's going to go after in rivers,
in particular for us here in the Mississippi River,
and that has really large-scale ecological consequences.
One of them is the formation of what we call dead zones.
So what that image represents in green,
these are the sites where of intensive use of fertilizers.
In pink that represents nitrogen coming from human activity
and from cities in particular.
But all that nitrogen ends up in ground water,
ends up in the Mississippi River
and ends up fairly rapidly in the Gulf of Mexico.
In the Gulf of Mexico what it's causing
is that all that nitrogen, all that nitrate
is feeding the growth of algae.
These algae consume oxygen and you end up with a region
that has very low oxygen levels
that basically cannot sustain any other form of life.
Fishes in particular cannot grow because
of these algae blooms.
And that dead zone, which is in the Gulf of Mexico,
is a direct consequence of the intensive use
of fertilizers in the Midwest.
Well, that's not the only place in the world at all
where we have dead zones.
There are dead zones around Europe, around France.
Now, massive dead zones around China,
but all that is due to our human activity.
That's one consequence,
there is also even more global consequence of fertilizers
on global warming because one product of degradation
of nitrogen to soil is nitrous oxide,
it's a greenhouse gas, which is also massive
and major component of global warming.
So now, all these are ecological consequences
of our intensive use of fertilizers.
So, on one hand fertilizers are great.
They are feeding half of the world.
On the other hand, their intensive use has a lot
of health, economical and ecological consequences.
And that's the kind of problem that we have here
in developed countries.
In the opposite spectrum, for developing countries,
their problem is that they simply cannot afford fertilizers.
In fact, in many developing countries the problem
is just to get a bag of nitrogen fertilizer
to the poor farmers.
And what I show you here, before I freak out, in particular,
it's a map that shows the places in the world
where corn production is limited by nutrient availability.
So, everywhere you have a green dot, it means
that we can reach 50% or more of the possible yield
we can get with the corn.
You see in the U.S., in the Midwest
or in Europe, no problem.
We use a lot of fertilizers.
Most of the time we can reach 50 or most this maximum yield.
But in places like Africa, in particular,
you see where you have red dots or blue dots,
these are limited in nutrients and the main nutrient
which is limiting in these places, it's nitrogen,
the second one would be phosphorous, but the main one
is clearly nitrogen.
So, for these countries, for these developing countries,
their problem is to get that fertilizer
and to have access to nitrogen fertilizers.
So, nitrogen fertilizers are a great thing but here
we have too much of a good thing
and over there they cannot actually get it.
So, that's the kind of problem that I think
we can help solving or at least alleviating with microbes.
I'm gonna talk about two types of microbes.
Some microbes that help the plants getting nutrients
from the soil and getting nitrogen, in particular,
from the soil and phosphorous too,
and I'm gonna talk about microbes
that help the plant getting nitrogen from the air,
which is even better.
So that's my introductions to these different microbes
that I'm going to talk about today.
On one hand, we work with microbes
that we call mycorrhizal fungi,
that is what is on the right part of my figure.
These fungi colonize the roots and extend
their high feet into the soil
and they help the plant getting nutrients and water.
They really help pumping these nutrients out of the soil,
and help the plant accessing these nutrients.
On the left part of my slide, I'm talking about bacteria,
bacteria that can do something called nitrogen fixation,
which is to convert nitrogen from the air into ammonium,
exactly the same process as this Haber-Bosch process
that I mentioned before, the chemical process,
except that here you don't buy bacteria,
or living organisms.
Same idea, you take nitrogen from the air
and you give it to the plant.
So, I'm gonna give you a quick introduction
about both types of relationships.
These first fungi, the mycorrhizal fungi,
when we say mycorrhizal fungi it encompasses
a wide range in fact of associations.
We classify them into you can see
these five different categories
of associations between plants and microbes.
The ones I'm going to talk about mostly today
are the ones on the right called, arbuscular mycorrhizal.
And the reason I'm going to focus on that one,
and we also focus on that a lot on our research,
is that these arbuscular mycorrhizal fungi can colonize 80%
of plants and the vast majority of our crops,
so these are in agriculture, for us these
are by far the major players.
You have other called ectomycorrhizal fungi.
Maybe you have heard about these ones.
These are those that you find in forests.
These ones are important, for instance,
for poplar production or pine production.
You go to any forest, the underground
is full of these ectomycorrhizal fungi.
Ericoid mycorrhizae, that one is a bit special to Wisconsin,
because that's a mycorrhizal fungus
that associates with cranberries,
so it has a very narrow host.
Really, it's about berries.
So, ericoid mycorrhizae,
honestly not so many people work on ericoid mycorrhizae.
A lot of the research is done on the arbuscular mycorrhizae
because these ones, as I said, colonize most of our crops.
These arbuscular mycorrhizae are very ancient.
These are very ancient association
between plants and microbes.
The characteristic of these arbuscular mycorrhizal
associations is what is how you on the right,
are these fungal structures that
are in blue called arbuscules.
And these structures are fungal structures,
highly ramified fungal structures that help increase
the surface of contact between the plant and the microbes.
Now the site where these nutrient exchanges
that I'm gonna talk about take place
and are very typical of these mycorrhizal associations.
When we see such a structure, we know
that we have one of these arbuscular mycorrhizal fungi.
On the left part of my slide, what I show you is a fossil,
a fossil which is 400 billion years old,
and 400 billion years ago what happened is that the plant
started to colonize land, so this is a fossil of one
of the first, some of the first land plants,
and inside of these fossils
we find arbuscular mycorrhizal fungi.
Many of us that study the evolution of these associations
think that the ability of plants
to associate with these fungi allowed,
in fact, plants to colonize land.
It's because plants were able to associate with these fungi
and use these fungi to extract nutrients from the soil,
that they have actually in fact been able to colonize land.
So when we think about these
arbuscular mycorrhizal association,
we often refer to the mother of archebiosis
because it's a very ancient association between plants
and microbes, and later, I won't have time to talk
about that today, but when plants want to associate
with other microbes, they often use actually mechanisms
that they initially developed to associate with these fungi,
so plants have developed initially that association
with these mycorrhizal fungi and then used these mechanisms
over and over to associate with beneficial microbes.
I'm gonna show you a quick movie
about what I show you here in white it's one
of these mycorrhizal fungi in yellow these are plant cells.
As soon as one of these fungi starts touching a plant cell,
within just a few minutes you can see that the nucleus
of the plant cell is gonna move right under the point
of contact with the fungus, and then you see that nucleus
moving down and it's followed by a tube,
an empty tube in fact, and that empty tube is the path
that the fungus is gonna use to penetrate inside
of the plant.
Once the tube is ready, then the fungus
is gonna penetrate inside of the plant cell.
That process is really driven by the plant.
The plant prepares the path for that fungus to colonize
and then it goes through the plant cells,
literally through them, it's a tube within the plant cell.
Then typically the fungus as you can see goes
between the plant cells in the inner part of the root,
what we call the cortex, and its within that cortex
that these fungi are gonna form what we call
these arbuscular structures that I showed you,
with a process which is very similar again driven
by the plant you see the nucleus starts to enlarge
and then the nucleus is gonna move again
and create that tube inside of the plant's cell
inside of which the fungus is gonna penetrate.
So in that process, the path of the fungus
is really guided by the plant
and it's really mutual communication and mutually
some of my colleagues refer to mutual dance
between the plant and the fungus,
there to establish that kind of association.
I think it's fairly intuitive that if you want
to have such a high coordination between the plant
and the fungus you need to exchange signals all the time.
The plant needs to know that that fungus is not a pathogen,
that it's totally okay to create a tube inside
of a cell to accommodate the fungus.
And that's really what we're talking about when we talk
about these sweet talks, about how the plant
and the microbe communicate because in order
to establish such a complex dance, if you want,
you really need to have the plant and the fungus communicate
all the time and exchange signals in order
to recognize each other.
So that's my introduction for you to give a feeling
of what we talk about, what we're thinking about
when we think about signal exchanges.
We need the tight coordination between the plant cell
and the fungus in order to have these associations.
Once these associations are established
then you can have exchange of nutrients,
in particular through these structures
that we call these arbuscules.
What I show you here in this figure,
I'm not gonna go into the details of all these transporters,
but on the right part that represents the soil,
the center that's the fungus and on the left,
that's the plant.
And at the interface between the fungus and the soil,
you have these transporters that many of my colleagues
are studying that help the fungus getting nutrients
out of the soil.
You have transporter for phosphorous
that have been very well-categorized, transporters
for ammonium nitrate, amino acids or urea,
which are sources of nitrogen.
So really the fungus is pumping all these nutrients
from the soil, transporting them to the plant
and on the left part of my figure, these are what happen
at the interface between the fungus and the plant
where again, what's going to happen is the fungus is going
to transfer that phosphorous taken from the soil
to the plant, nitrate ammonium nitrogen is gonna
be transferred and at the bottom of the slide
you have the reward, if you want, the plant rewarding
the fungus for providing nutrients in the form,
in particular, of glucose and fructose sugars.
So that's typically the kind
of nutrient exchanges that take place,
and a lot of us study how these
nutrient exchanges are regulated.
That's for the association between plants
and mycorrhizal fungi.
On the other side of my slide I'm talking
about associations with bacteria
and these nitrogen-fixing bacteria, so the process
of nitrogen fixation is the one I mentioned before
of transforming, converting dinitrogen in the air
into ammonium, and that process
is very important ecological process.
What I show you here that what we call the nitrogen cycle.
In the nitrogen cycle you can see that we have a lot
of nitrogen in the air, in fact 80% of the air
is composed of nitrogen.
That nitrogen unfortunately is not accessible directly
to the plant.
Plants cannot access directly that dinitrogen in the air.
In order to get that nitrogen, it needs to be
in the form of ammonium or nitrate, mostly nitrate.
I mentioned what is on the right,
what I call industrial fixation, which is that process
where we use natural gas to convert that dinitrogen
into ammonium and then that nitrogen is used as fertilizers,
but what I'm gonna talk about now is the process
on the left called biological fixation.
Biological fixation is when this process
is realized by bacteria in particular
that can convert dinitrogen into ammonium.
This conversion of nitrogen into
that biological nitrogen fixation
is extremely extremely important in terms of numbers.
I'm not gonna talk about what is called
atmospheric fixation, which is done by lightning,
in fact every time you have a lightning, it converts
a little bit of nitrogen in the air into ammonium.
Well, as you can see, lightning are responsible
for about 10 million tons of nitrogens fixed per year.
Biological nitrogen fixation on land
is about 90 to 140 million tons.
If you go to the bottom of the slide, industrial fixation,
the Haber-Bosch process that I mentioned,
is about 80 million tons per year.
So when you think about scales, it means that
we produce almost as much as fertilizer
as biological nitrogen fixation on land.
So we can think about how that chemical process also
is gonna disrupt the global nitrogen cycle.
Of course what we would like to do is to shift the balance
and to be able to take much more advantage
in or agriculture of biological nitrogen fixation
to limit our dependence on nitrogen fertilizers.
I really don't think that we can totally eliminate
nitrogen fertilizers at all, but it's a matter
of using less of them and taking more advantage
of biological processes.
The enzyme in bacteria that performed that conversion
of dinitrogen into ammonium is called the nitrogenase,
and that enzyme is again gonna take dinitrogen
which is N2 here and convert it into ammonium.
In order to do that process, that enzymes requires
a lot of energy in the form of ATP.
You see 16 ATP molecules required for the conversion
of one molecule of dinitrogen
into two molecules of ammonium.
16 molecules of ATP, it's a lot of energy for a cell.
That process of converting dinitrogen into ammonium
is very expensive in energy.
Whether we do that with bacteria or we do that chemically
with natural gas, it requires a lot of energy.
So one of the problems, if you want, that we need
to solve when we want to improve, take better advantage
of these associations is to make sure that these bacteria
have an abundant energy source because
it's a very energy-intensive process.
Another issue that we need to solve
in biological nitrogen fixation is the problem of oxygen.
This enzyme is highly sensitive to oxygen and so
in every system that you have that is efficient,
is performing efficient, biological nitrogen fixation
you have a way to protect that enzyme against oxygen.
One of the most, or if not the most efficient system
that have been developed for evolution
is the association between plants of the legume family
like soy beans, alfalfa, peas, beans and bacteria
that we call rhizobia.
And these associations lead to the formation
of new organs on plant roots that we call nodules.
I don't know if you dig soy bean root or an alfalfa root
you will often see these small little bumps
on the roots that often are pinkish and these
are what we call these nodules.
These are little, if you want, houses where the plant
is gonna house these nitrogen-fixing bacteria
and solve the two problems that I mentioned before,
solve the problem of energy.
These plants are gonna feed the bacteria with sugars inside
of these nodules, and the problem of oxygen,
they protect these bacteria against oxygen
so that they can fix nitrogen.
I'm not gonna go through all the details of that cartoon,
but that cartoon represents the different steps
of the dance in this case between bacteria
and plants to lead to that formation of nodules.
What that represents, it's a legume root,
if you want a soy bean root, where the bacteria
are gonna come in contact with the root hairs.
The root hairs are gonna curl around the bacteria,
enter the bacteria and form these tubes inside
of the plant cells to guide again the bacteria deep inside
of the plant root.
And in parallel, you have the development of these organs
that I'm calling the nodules inside which the process
is gonna take place.
There is a very striking similarity in the process
in the colonization process in that association
and the one that I mentioned before,
the mycorrhizal association.
It's actually from an evolutionary point of view,
we know that legumes accommodate these bacteria,
these rhizobia using processes that initially
had been developed to accommodate the fungi,
these mycorrhizal fungi.
That's the same process, the plant creates a tube inside
of the cell to allow, to give a path
to these microbes to colonize.
So again, for that association, it really requires
a tight coordination between the plant
and in that care, the bacteria.
It requires a lot of signal exchanges.
That for the communication part, for the nutrient exchanges,
I'm not gonna go into the details of all these metabolize,
but the main message here is that the deal if you want
is that these bacteria fix nitrogen, they have that enzyme
the nitrogenase, and they are gonna export that nitrogen
in the form of ammonium, that's the line at the bottom
in blue, or in the form of amino acids,
these are the transporters in yellow.
So the bacteria get nitrogen from the air, make ammonium
and give that nitrogen to the plant and the deal,
if you want, in return the plant is gonna provide malate
as a carbon source.
So here these are not sugars, these are diabolic acid
like malates, but the deal is the same.
The plant is feeding the bacteria with a source or carbon.
So that's the kind of nutrient exchanges that take place.
So that was my introduction to these associations.
On one hand, mycorrhizal associations that you can find
in the vast majority of crops, in corn, soy bean, alfalfa,
many, tomatoes, potatoes, whatever.
Most of the crops are able to associate
with these mycorrhizal fungi and on the left,
nitrogen fixing bacteria.
There it's mostly limited to legumes
like soy beans, soy beans, peas, beans.
That's why in agriculture we rely so much on legumes
in any sustainable system in agriculture we always need
to introduce a legume and the reason why we always want
a legume, particularly here in the Midwest,
is the corn soybean rotation.
The reason we want soy bean is because of that process
of biological nitrogen fixation.
It's because these soy beans can get their nitrogen directly
from the air without the need for input,
without the need for fertilizers.
So that's the introduction.
So I'm gonna talk now about I would say more
the core research of what we are doing in my lab
as well as in other colleagues are working on too,
about what I call the sweet talks and trade deals,
which is how plants and microbes can talk to each other,
how they can recognize each other, how they can do
that little dance of associating together
and how they can regulate these exchanges of nutrients.
Another way to think about the sweet talks, if you want,
is how do you recognize your friends.
How plants can differentiate beneficial microbes
with other microbes of fungi
or these rhizobia from pathogens.
How the plant, why the plant is gonna create these tubes
inside of the plant's cell for the beneficial microbe
and not for pathogen.
So what we're working on there are signal exchanges
and typically what has been found over the last years
and decades of work is that on the left part, for instance,
of my talk between plant and mycorrhizal fungi we know now
that the signal from the plant to the microbe,
the main signals are called strigolactones.
They are in fact plant hormones that plants release
through their root exudate in the soil.
And these signals are gonna trigger the production
of factors that we call myc factors or mycorrhizal factors
that then the plant is gonna recognize.
So it's really a communication system.
The plant is producing a signal saying I'm there,
really what strigolactones mean is I'm there.
The plants say, I am looking for hosts,
in fact strigolactone is increased when plants
need mycorrhizal associations.
And in return, when you have a fungus present, the fungus
is gonna produce these myc factors to say,
hey, open the door.
On the right part of my slide, it's a very similar dialogue.
It's again, it's a molecular dialogue where there
are plants and microbes talk with molecules.
There, the legumes produce flavonoids, isoflavonoids,
compounds which are going to be recognized
by these rhizobia bacteria.
And these bacteria, in return again,
are gonna produce signals that we called nod factors
for nodulation factors.
So when the signals are coming from the microbes
we call them mycorrhization factors
or nod factors, nodulation factors.
What is interesting for us in that dialogue,
in that signal exchange, is that nod factors
and myc factors are in fact very similar.
Nod factors are molecules that we
call lipo-chitooligosaccharide.
Of course I don't want you to remember the structure,
we call them LCOs.
They are, if you want, a keratin backbone and a lipid.
Interestingly for us, just a few years ago it was found
that the signals form the fungi are again
what we call myc factors,
are again lipo-chitooligosaccharides, these LCO molecules.
Not exactly the same structure, but very similar molecules.
So what that means on the global scale is that for
from the plant perspective, whether your friend
is a fungus, is a mycorrhizal fungus or the friend
is these rhizobia bacteria that take nitrogen,
the signal they perceive are very similar.
What these LCO signals mean to the plant
is I'm a friend, which is a great thing.
It's great for us because now we know what kind
of signals microbes use to say, I'm a beneficial microbe.
So if you think about it, on one hand it's great because
now we have each one the golden key to allow microbes
to associate efficiently with crops, and so you think,
oh great, we can help increase, improve association
between crops and these beneficial microbes.
That's true.
On the other hand, that can be scary because you think
hey, maybe some microbes are gonna find a trick,
some microbes are gonna use these LCO molecules
to trick the plant and try to be a pathogen.
So imagine that you have a microbe which is a pathogen
that produces that kind of signal, they have the golden key
to colonize a plant.
They can trick the plant and tell the plant they
are a beneficial microbe when they are not
and that's really where my second part of the think
we are interested called the trade deals are important.
Cause these trade deals, their goal is to deal
with cheaters, to deal with microbes
that would trick the plant, that would say
I'm a beneficial microbe, but without providing any benefit.
Imagine that one of these fungus or bacteria
can penetrate inside of a plant and do nothing except grow.
That's not what you want.
That's not what the plant wants.
The plant needs to have a system to deal with the cheaters,
and these are actually very interesting stories,
very briefly that I'm gonna talk about.
When I was talking about the signal exchanges,
the striking feature is that the signal
is pretty much the same whether it's coming
from these fungi or the bacteria.
They are these LCO signals.
When it comes to dealing with cheaters the strategies
that plants employ are very different.
First, in associations in between legumes and rhizobia,
what the legumes are doing, like soy beans, or alfalfa
is doing, is what we call a sanction mechanism.
It means that the plant is gonna kill the
nitrogen fixing bacteria that are not efficient.
If you have some of these bacteria that produce the LCOs
but do not fix nitrogen efficiently,
they are gonna be killed by the plant
and these are very interesting experiments
that were performed by a colleague in Minnesota where
what you see on the left are, I don't know if you can see,
but you have a root with small nodules
and on top you have these fancy equipment that
is used to control the atmosphere around the nodules.
And what they are doing here is that they are tricking,
they are using a trick to prevent these
nitrogen fixing bacteria from fixing nitrogen
by replacing the atmosphere around the nodules by argon.
So in the air what you have it's in the right in the air
in black, normal air has nitrogen and oxygen.
If you replace the nitrogen by argon,
the bacteria cannot fix nitrogen anymore
and that's a trick that we use to prevent some nodules
from fixing nitrogen whereas we can allow the nodule next
to it to still fix nitrogen.
What happens when you replace nitrogen
so the black with argon, the gray one,
is that what you see on that graph is a decrease
of the number of rhizobia inside of these nodules.
In other words, when you prevent these nodules
from fixing nitrogen if for any reason one
of these nodule structure on the soybean roots
don't fix nitrogen, then the plant
is gonna kill the bacteria inside of it.
And that's a sanction mechanism, and it's very efficient,
you can imagine, at selecting cheaters.
Only the bacteria that can fix nitrogen properly
inside of this structure will be able to grow, multiply
and later be released into the soil,
whereas the cheaters, of course they can go
into these modules but they are going to be killed
by the plant.
So, in that plant bacteria association,
it's a sanction mechanism.
Totally different from what we see
in mycorrhizal associations and that is I think beautiful.
There, that mutualistic association is stabilized
by rewards system, in fact it's a mutual reward system.
The plant is gonna reward the good fungus and the good fungi
are gonna reward the good plant, and what I show you here
I experiment so the top part of that experiment
were performed by a colleague,
a fantastic colleague, Toby Kiers.
What she did is that on top you have a system
with three compartments.
You have a root compartment
and then two fungal compartments on the right
and on the left.
On the right fungal compartment, these fungal hyphae
have access to phosphorous, they can get phosphorous.
On the left, they cannot get phosphorous.
So what happens here in that system is that both fungi
those that can access phosphorous
and those that cannot can colonize the same plant.
And what she's doing is that she's monitoring how much sugar
that plant can give to the fungus by using (mumbles).
And what you have on the right, what this shows
is the amount of sugar that the plant gives
to different fungi.
On the fungi that cannot provide phosphorous
or have zero micromolar, you see far less sugar given
to that fungus than to the fungus that can have access
to have nitrogen whether it's 35 micromolar
or 700 micromolar of phosphorous.
What that means here, is that when the plant has the choice
between the fungus providing phosphorous
and the fungus not providing phosphorous,
the plant is gonna give its carbon
to the fungus providing phosphorous.
So the plant is gonna reward the fungus giving it benefit.
Reciprocal experiment that the top bottom part of my slide,
again, that's the same design.
Three compartments except here it's one fungus
and two plants, two root systems, one root system
on the right that can provide sugar and one root system
on the left that cannot, and what she measured here
is how much phosphorous is given by a specific fungus
to two different root system, a root system
that can give sugar and a root system
that cannot give sugar.
What she observed that's what is on the right
is that the fungus is gonna give it's phosphorous
to the root system that can provide the sugar.
So in other words, this fungi when they have access
and that's the case in nature, these fungi
can colonize many plants at the same time, these fungi
are gonna give their phosphorous to the plant
providing the more carbon.
It's a reward system, and so you have
that mutual reward system where the plant rewards the fungus
that is providing the most benefits
and the fungus rewards the plant
that provides the most carbon.
So it's that mutual reward system that stabilizes
that association and makes sure that you avoid cheaters,
because only the most performing partner
is gonna be rewarded.
So that's really what we study when we study
these trade deals, and how we deal with cheaters.
So that's pretty much what we are doing in my lab,
working on these signal exchanges that the sweet talk,
how they can recognize their friends,
and on the right, how they deal with cheaters.
Briefly, with the time I have left,
I'm gonna talk about applications.
Some of these applications are what I call
the low-hanging fruit, that are the practical applications
of how we use these microbes in the field.
These microbes, many of these microbes are used
and commercialized as inoculants
If you buy beans or peas for your garden,
you often find next to the seeds, you can finds bags
of rhizobia which is sod, and these rhizobia
are applied typically on the seeds before planting.
Soy bean farmers know very well that they need
to inoculate fairly frequently with these rhizobia.
In fact, I have a piece of the Wisconsin State Journal
from 1906 recommending to farmers to inoculate their seeds.
The University of Wisconsin has been one of the first ones
providing their farmers with these rhizobia inoculants.
At the time, in the beginning of the 20th century,
it was top technology.
Now it's widely used.
What we're currently doing with that kind of technology,
is try to evaluate when these products,
whether they are rhizobia inoculants
or mycorrhizal inoculants, when they're really useful
for the farmer.
When do they really need them, when they don't need them.
Mycorrhizal inoculants, in particular, are pretty expensive.
The rhizobia one, they are pretty cheap,
but in both cases what we are doing is try
to inform the farmer about when these products are useful,
when they are necessary, what are the best products
on the market.
So that's I would say a very direct application of the work.
A bit more development side, I mentioned
that these NaCL-molecules that
are these key signals produced by these rhizobia
or these mycorrhizal fungi.
In fact, for about 10 years now, almost 10 years,
these NaCL molecules have been commercialized
as plant growth promoters.
In fact, what these signals mean to the plant,
is that you have beneficial microbes around,
and one direct consequence of that on the plant,
is that the plant is gonna grow faster.
The plant thinks that you have beneficial microbe
it's gonna develop, in particular, its root system
to be colonized, so we treat the plant but that has
a direct consequence, in particular, that really helps
for establishment, for crop establishment.
Sometimes the crop is gonna grow a bit slowly
at the beginning of the season.
If we treat with these products, the crop
is gonna grow much faster at the beginning.
And that directly translates into here.
So what we are doing is working on one hand,
we are finding more of these structures
of this NaCL molecules and we find things that work better,
and on the other hand, we also work on efficiency,
on when these products are useful for farmers
and when they are not so useful, and so we try
to give some guidance of when they should be used
and when that's not necessary.
So all these are direct consequences of the work we do
on these bacteria, on these bacteria rhizobia,
on these fungi because we have commercial products available
we try to inform the farmers
and possibly develop new products.
More long term application of what we are doing
is to study evolution and to study
how these associations evolved and in particular things
that we're really excited about is to understand what
are the critical innovations, what happened
during plant evolution that allowed plants
to form these arbuscular mycorrhizal associations
150 million years ago.
So what I show you here, it's a very simplified tree,
phylogenetic tree of land plants and at the base
of that tree you have these
arbuscular mycorrhizal associations because as I told you,
plants as soon as they started colonize land,
they started forming these associations, so the kind
of research we do is, for instance, comparing algae
to some of these most basal land plant called liver warts,
and figuring out what happened,
algae do not form mycorrhizal associations, liver warts do.
What happened at that point of time that allowed plants
to form these associations.
And eventually later, during plant evolution
what happens in legumes.
Why legumes got the ability to associate
with these rhizobia, whereas for instance, corn
or cereals cannot, and the reason we are so interested
in evolution is that these evolutionary information
can guide our engineering projects, and that's really
why we study,
evolution is interesting in itself of course,
but also it has some practical applications.
We can use that information to engineer,
to create new things.
Legumes are going to associate with rhizobia.
Cereals like corn, wheat, rice
cannot associate with rhizobia.
Can we transfer that ability to associate
with nitrogen fixing bacteria from legumes to cereals,
in particular, and that would be fantastic
because that would help reducing our dependence
on nitrogen fertilizers.
And so that's my, I think it's a pretty cool slide.
It's my yes we can.
That's the slide I was using to try
to convince the community that yes we can engineer
symbiotic associations, and that's really one
of our major goals here is to try to improve
the associations between cereals, in particular,
and nitrogen fixing bacteria.
In agriculture, growing corn is one of the major reasons
why we use so much fertilizer.
Cereals require a lot of nitrogen fertilizer
and if we could at least alleviate the dependence,
reduce the dependence on nitrogen fertilizers
then we would really have a big impact.
So that's the kind of project
that we're really excited about.
It's funded both by the Bill and Melinda Gates Foundation
and the reason they are really funding that kind
of project is in particular for Africa and for poor farmers.
I was mentioning at the beginning the problem.
First, the problem here is that we use too much fertilizer.
For them in Africa, the problem is access to fertilizer,
so the Gates Foundation is funding that kind of project
in particular to alleviate the need
of fertilizers in Africa.
And the NSF, National Science Foundation,
is also funding that kind of project.
Of course it's really long-term but I think for us
it's really the Holy Grail.
That's really what we want to achieve in the long term
is to allow cereals to grow with less fertilizers,
and that's really where we think we can
have an impact on agriculture.
Alright so that's the overall view of what I talked about.
I just want to take a few seconds
to acknowledge my lab members, the people doing the work;
Funding is coming from NSF, the DOE, and the USDA,
and the Gates Foundation;
and all these great students
that I have the chance to work with, as well as colleagues
who are right here on campus from very different discipline,
from biochemistry to microbiology and plant sciences.
It's a really interdisciplinary work.
We work with plants, we work with fungi,
we work with bacteria and we take that from different angles,
and one of my students is here actually, in fact, in the room.
Alright?
So, thank you very much for your attention.
It was pleasure to be here.
(applause)