Nick Talbot,  University of Exeter

Nick Talbot, University of Exeter

August 27, 2019 0 By Stanley Isaacs


– Thank you very much for the invitation, I’m really very pleased to be here. What I’m gonna do is continue
telling you about this really significant disease
of rice blast disease, and of course as we’ve heard, it’s also a significant threat
to wheat production as well. What I’m gonna do is try and
try and tell you some work which is somewhat
complementary to the studies that Barbara has talked
about, and tell you much more about the developmental
biology of the fungus, and something about the underlying determinants of virulence. So how is this fungus
able to cause disease in rice, and indeed in wheat? Okay, so, you can see
the typical leaf symptoms on these raw mature rice leaves. And I think the important thing to say is this gives you an idea of how this disease can build such enormous disease pressure, and reach epidemic proportions. These lesions are about a
centimeter or so in length, and each one of those lesions will produce somewhere between 20 and
50,000 spores every 24 hours. Sporulation is almost circadian rhythm, so this sporulation
occurs at the dew point, which is the ideal opportune time by which transmission can occur. And you can imagine that
they’ll continue sporulating every 24 hours for several weeks. So you can have enormous inoculum build-up of the spores that transmit
this fungus very, very quickly. But the disease that pathology, that farmer’s fear the most is this one, is neck blast, and as Barbara mentioned, when this spreads into the panicle, or into the neck, which
holds the inflorescence, the panicle which holds rice grain, you can get complete yield loss. And this picture was taken
in Hunan Province, in China. So I took this picture
around 10 years ago now, and I spoke to the farmer then. The farmer said they had about 80 to 90% yield loss for
that particular field. So you get absolute
devastation when you get neck and panicle blast symptoms occurring. And of course, in wheat blast, the symptoms are, again, very different. It’s a spike disease, it resembles diseases that other plant pathologists will be familiar with, things
like Fusarium head blight. It actually looks like a very
different type of pathology. So this fungus actually
has the capacity to grow in very, very different tissue types. So it can grow in stem tissue,
it can grow in leaf tissue. We also know it can grow
even in root tissue, and it has an ancestral
relationship to root pathogens like Gaeumannomyces
graminis, for instance. So it has the capacity to
actually colonize many, many different parts of plant tissue, and indeed cause very
different pathologies. And as Barbara mentioned,
wheat blast is now a really significant
threat to wheat production across South Asia, because
of its movement there in the last year, and when a disease is sufficiently destructive,
that the only means of controlling it is to
throw kerosene on the fields and set fire to it, you can see that this is actually an urgent problem. One which we in the
blast research community really have to take
some responsibility for, and the next speaker, Sophien Kamoun led the Open Wheat Blast
Project, by which a group of blast researchers around the world really try to respond very, very quickly to this emerging threat in wheat blast, this threat to wheat production. Okay, what I’m gonna do,
though, is tell you about what we’re trying to
do to try and make sure our rice looks like this, rather than it looks
in its diseased state, and I’m going to tell you about three different things today. So first of all, I’m
gonna tell you about how the blast fungus actually
infects rice plants. I’m gonna tell you about
the very early stages of infection, right at
the start of the process. Then I’m gonna tell you
some new work about how the blast fungus is able
to move between rice cells, and that’s going to
include an understanding, or a development of some of the things that Barbara talked about
in terms of manipulation of plasmodesmata, those
channels between plant cells. And then finally, we’re gonna talk about some of our applied work,
what we’re trying to do to control rice blast
in the developing world, and some of the work
we’ve been doing there. Okay, so how does the blast
fungus infect rice leaves? Well, the disease cycle
starts when these three-celled spores land on the surface of a rice leaf. They carry with them their own adhesive, their own attachment
factor, which is released upon hydration, sticks
the spore very tightly to the hydrophobic waxy
cuticle, and the spores will then immediately
germinate, and they send out a polarized germ tube, which will then quickly differentiate within
a small number of hours, within about four hours,
into a dome-shaped cell called an appressorium. This appressorium is
the infectious property, or the infectious cell from
which all the subsequent fungal material will be derived. This single dome-shaped cell,
which the fungus then uses to penetrate the cuticle. And there are several,
there are essentially three prerequisites for appressoria to form, and then to function properly, and I’ll tell you briefly about those. The first thing is this has to be on the appropriate surface. Appressoria will only form on
a hard hydrophobic surface, and the fungus will respond
to waxy cuticle components from the rice leaf surface. To do that, they utilize
the signaling pathway, or these two signaling pathways. First of all, there’s a very conserved mitogen activated protein kinase cascade, the Pmk1 pathway, and this
responds to upstream receptors, there’s G-protein coupled receptor, which can respond to ligands
of the rice leaf surface, and there are also a
series of stretch activated gated iron channel
proteins, which can respond to the hardness and
hydrophobicity of the surface. That will trigger morphogenesis, it triggers appressorium formations, such that if you delete
that single MAP kinase Pmk1, the fungus is no longer able to make an appressorium properly. At the same time, there’s
trafficking of the contents of the spores into the appressorium, and control of appressorium turgor, and that is the responsibility
of this pathway, the cyclic AMP response pathway, which actually leads to a
number of those changes, particularly in terms of
cellular storage products, things like lipid body movement, and lipid body degradation,
and also glycogen degradation, and the whole control
of primary metabolism, which has to be radically changed during appressorium morphogenesis. The second thing has to occur
that this is very tightly controlled to cell cycle
control mechanisms, and you can see that illustrated here. This is a three-celled conidium. This nucleus here will divide in a moment, see there it goes, and the formation, the initial formation of
that cell is determined by a cell cycle control point,
as an S-phase checkpoint. Then these nuclei left in the
spore will start to degrade, that one goes first, followed
by this one and this one. So, cell cycle control
is usually important. That three nuclei to four
nuclei, to one nucleus pattern, is completely invaried. Every time there’s an infection event, it always goes through
that chain of events. And there are a series of
cell cycle checkpoints. There’s an S-phase checkpoint, the DNA replication checkpoint, which determines the initial
swelling of that cell. The appressorium won’t
become fully differentiated until that nucleus is
actually passed through from G2 into M, is
actually undergone mitosis, and the mitotic exit is actually important for appressorium maturation to occur. Indeed, there’s a second
S-phase checkpoint that’s really important, subsequently, for repolarization, as
I’ll tell you about later. So there’s a series of
cell cycle checkpoints control appressorium morphogenesis, and also, importantly, those three nuclei have to have been degraded
in order for this cell then to be mature and competent to infect rice. And that process involves autophagy. So here is a wild type
cell, and you can see the single nucleus in
each of these appressoria. This is a mutant where we’ve deleted one of the components of the
macro autophagy pathway, ATG8, and you can see that the
nuclei no longer degraded, so they’re distended, and
they’re abnormal in shape, but they’re no longer degraded. And what happens under
those conditions is that the appressorium, although it forms, it is unable to mature properly, and it is unable to repolarize. So there has to be
recycling of the contents of the spore, including
breakdown of the nuclei, as a prerequisite to
make this appressorium functionally competent. And that’s because this
appressorium has to generate enormous turgor, so it can generate turgor of up to 8 megapascals,
so 80 bars of pressure, 40 times a car tire, so an extraordinary pressure for
a living cell to generate. And it does that by accumulating solutes, polyols including glycerol, to extraordinarily high concentrations. That draws water in by osmosis, and the solute is prevented
from leaving the cell, because there’s a thick melanin layer in the dome of the appressorium. So it’s a combination of solute
generation and melanization, which make that appressorium
able to generate such enormous turgor,
which is then applied as physical force to
puncture the rice cuticle. And we know that the
Magnaporthe is perfectly capable of breaking inert surfaces, it can break thin plastic
layers, for instance, so it doesn’t need to use
enzymes to degrade the cuticle, it can do this using physical force. So the appressorium itself has to apply its penetrative force at a single point at the
base of the appressorium, the appressorium pore. So that leads to a whole
variety of questions about how the fungus is able
to change its axis of polarity, and how it’s able to then
gain entry to rice tissue. And some years ago, we
started studying this process, and we started to look
at the reorientation of the actin cytoskeleton. What we found is that at
the base of the appressorium a toroidal ring structure of
filamentous actin is found, and that’s scaffolded and held in place by the formation of a septin ring. So septins are GTPases which form hetero-oligomeric structures, that are obviously well
known to people here. Jeremy Thorne is in the audience, so lots of you will be
familiar with septins. So septins are pivotal to a
whole variety of different morphogenetic processes, in funginals and in mammalian cells, for instance. What septins are doing
here is acting as a means of actually developing cortical rigidity, but they act as a diffusion barrier for polarity determinants,
which are the means by which the appressorium
is then able to repolarize. And you can see that the septin ring, and this is an enormous septin ring, it’s about 5 micrometers in diameter, it colocalizes with actin at
the base of the appressorium. And this is the precise
interface where the appressorium is in contact with the rice leaves. If we swing the microscope slide, you can see this is the interface, the point at which the fungus is going to penetrate the underlying leaf tissue. If we delete any of the four core septins in Magnaporthe, then
that filamentous actin toroidal structure can’t form properly, you get this tangled mess of actin fibers, but they’re unable to
form that ring structure at the base of the appressorium, to organize the appressorium
pore structure properly. The septins are also
responsible for the organization of a whole variety of other
proteins, for instance, the eight membered exocyst complex, which is required for
polarized exocytosis, is also found in a ring
formation at the base of the appressorium, and that’s
a septin-dependent process, they’re held in place, they’re organized in a
way which is dependent on the activity of the septins. So how then does the appressorium perceive a signal to then repolarize? Well of course, one of the
things that’s occurring here is pressure generation,
and we know that if we artificially lower
pressure, which we can do by incubating appressorium
hyperosmotic concentrations of glycerol, for instance,
then this affects its ability to make these septin rings. This is actually a septin ring set five, and you can see in a control cell, we have septin ring formation
during a time course of appressorium development. But if we add hyperosmotic
concentrations of glycerol, then the septin ring
doesn’t form properly, unless the glycerol is
added at a very late stage, which a commitment point
has already been crossed, or if we inhibit melanization, which will also affect
the turgor of cells, then again, that has an effect on the organization of the septin ring. And all of the downstream
subsequent events to that are determined by the
cell having to achieved a threshold of turgor. And recently we’ve identified
a turgor-sensing kinase, the Sln1 histidine aspartate kinase, which seems to be imported
for the modulation of turgor, and therefore acts as a master regulator for these downstream processes, which lead to repolarization
of the appressorium. In an Sln1 mutant, which
is non-pathogenic on rice, if we measure the internal
pressure of the cells, we can do that by incubating
it in hyperosmotic concentrations of
glycerol, so 3M of glycerol would normally be sufficient to collapse almost 90% of appressoria
of the wild type cell, but in an Sln1 mutant
continually develops pressure. So it just develops pressure,
and pressure, and pressure, but is never able to repolarize. So it’s never able to
modulate that pressure, and convert that, or translate
that into physical force in the reorientation of the cytoskeleton, those regulatory processes
are unable to occur in the absence of this Sln1 kinase. And that’s enabled us
to put together a model for how we think appressoria function, and this is a model
that we’re busy testing. In that, we have Sln1 as
a turgor-sensing kinase, we know that it is
tethered to the membrane, and it’s associated,
it physically interacts with some stretch activated
gated iron channel proteins. It also acts upstream of
the cell integrity pathway, and the protein kinase C pathway, and acts as a means of
modulating melanin by synthesis, and also the cyclic AMP dependent
protein kinase A pathway. It also is responsible for activation of the NADPH oxidase complex, which leads to a reactive
oxygen species burst in the appressorium, and that in turn affects the regulation of
some polarity regulators such as CDC 42 and Rac1, and also the modulation of
turgor involves regulation of the glycerol efflux pump,
the Fps1 glycerol efflux pump, by which means turgor is being modulated. That leads to a series of
events, which ultimately will lead to, for example,
the septin ring formation, the remodeling of actin, chitin
and glucan synthase activity as the penetration peg is developed, and then targeted exocytosis at the pore, and then some endocytosis obviously, so we achieve membrane
homeostasis at that point. This is also subject to a
cell cycle control point. Only if that nucleus is passed
from the S-phase into G2 will the appressorium be
functionally competent, and that ultimately is what
leads to peg formation. So we’re beginning to
have an idea about the way appressoria function, and
we have a number of leads by which we can actually test whether some of these assumptions are correct, which is work that’s ongoing in my group. So what happens next, then? So this is working on
the rice leaf surface, what’s the next stage? What actually happens subsequent to that? How does the fungus
move between rice cells? What happens once it’s
actually in the rice leaf? And you’ve seen some of
the morphogenetic changes that occur once the fungus
is in the rice leaf, from Barbara’s talk. And as it’s now entering in this point, and moving into a primary invasive hyphae, and then colonizing tissue rapidly. So we can see here is an
appressorium if we lift the rice tissue, we can see
there’s the penetration peg, which is entering the
underlying epidermal cell. And those invasive hyphae actually change in terms of their shape, they
become bulbous branch cells, they’re undertakers of the
pseudohyphal type of growth, they actually grow with a
budding type of phenotype, rather than classical filamentous hyphae, which we see when we grow
the fungus in culture. And as Barbara mentioned, they’re bounded by a tight apposition to
the plant plasma membrane, so there’s a sealed hyphal
membrane compartment around the hyphae, and in
this case we’re looking at a rice transgenic plant,
where we’ve got GFP labeled plant plasma membrane
protein, you can see that the rice plasma membrane
tightly bound around this invasive hyphae, which is expressing cytoplasmic red fluorescent protein. And remarkably, as this fungus
moves from cell to cell, it’s able to maintain membrane integrity into the cells into which it’s moving. So as it vacates cells, so
you’ve got this initial cell that’s been invaded by Magnaporthe, very often we lose the
integrity of the membrane that surround those hyphae,
and eventually those cells will lose viability, and
that’s where you begin to see the beginning of the necrotic lesions, the symptom development of rice blast. But it’s continually
moving in a bitrophic way, it’s moving into living plant tissue, and as it moves into adjacent cells, it’s always bounded by
plant plasma membrane. So it’s maintaining the
integrity of the cells that it moves into, and the
way it’s able to do that is by manipulating plasmodesmata, and moving through pit fields to enable it to actually maintain
that membrane integrity of the cells into which it moves. As Barbara mentioned, there
are two different types of effectors, effectors
which are in the apoplast, that is green effect of
Bas4, which she mentioned, which is secreted from
hyphal tips into the space between the fungal cell wall
and the plant plasma membrane, and then there are cytoplasmic effectors which are released through
this BIC structure, this bitrophic interfacial
complex, and their destination is in the cytoplasm, or
in different organelles within rice leaf cells. So how then is the fungus able to regulate some of these processes? And in particular, how
is it able to regulate its ability to move from one rice cell to the next rice cell? Well, to study that, we
need to reintroduce you to this signaling pathway,
which we spoke about at the beginning of the talk, when I was talking about
appressorium morphogenesis. So, the Pmk1 MAP kinase we
know is absolutely essential for pathogenesis of the fungus, but if we just knock this
gene out, if we deleted them, we don’t see an appressorium, there’s no appressorium formation. But I remember that whenever you infect a wounded plant with the Pmk1 mutant, or indeed if you inject
spores into living tissue, this mutant is never
able to cause disease, at seemingly any stage. So we wondered whether
it actually played roles later on during infection. So we wanted to make a
conditional mutant to Pmk1 to try and address that. And the way we did that was to make an analog sensitive protein
kinase mutant in Magnaporthe. So we made a point mutation
in the gatekeeper residue of the ATP binding pocket of Pmk1, and we introduced the allele back into a Pmk1 deletion mutant, and it complements all of the mutant
phenotypes as you’d expect, but that point mutation is able to make that kinase sensitive to
this naphthyl PP1 molecule, and therefore provides you with a tool by which you can conditionally
inactivate the kinase by adding an inhibitor, which will only affect a single MAP kinase. And to check that that worked properly, we can see here’s the
complemented strains, so the Pmk1-AS is able
to make an appressorium normally in the absence of an inhibitor, but if we add an inhibitor, naphthyl PP1, then its ability to make
an appressorium is gone. But that means we can
now do the experiment which we wanted to do originally, which is to inactivate the
kinase after infection, find out what will happen if we inactivate this protein kinase once the fungus is in living plant tissue. Well, what happens normally
when we infect tissue, this is the Pmk1-AS strain,
but with no inhibitor, so this is what would
happen if a wild type cell infects the cells, you can see
it fills the epidermal cell, and as soon as it reaches
a sort of threshold of hyphae, it then breaks out, undergoes hyphal constriction, breaks out into the adjacent cells. It actually becomes more
polarized as it’s doing so, and it breaks up into the adjacent tissue, and this is how
Magnaporthe is able to move from one cell to another,
and you’ll see at the point at which it moves, there
are hyphal constrictions as it locates pit field sites, which are clusters of plasmodesmata, and then moves through
those into adjacent cells. So this is what happens
with the Pmk1-AS mutant, but in the absence of an inhibitor, so where the kinase is working normally. So if we add the inhibitor, the fungus is growing normally, and it will fill this epidermal cell, and it will carry on
filling this epidermal cell, but it will never escape from it, and it’s unable to move
out of that cell at all, and into the adjacent cells. So it will fill the epidermal
cell, but it’s trapped, and is unable to move
into the adjacent cell, and you can see that in this micrograph, it will fill this epidermal cell, this is an appressorium out
of focus on the leaf surface, this is the first epidermal cell, but it’s unable to move into any of the adjacent cells around it. By doing that, by becoming
trapped at that point, the plant is then able to respond, and the plant will launch
a defense response, and you can see that this is a reactive oxygen species burst, where we’ve stained with DAB staining, so we’ve been able to
identify a reactive oxygen species burst, a plant defense response, as a consequence of the
fungus not being able to progress into rice tissue. So what is Pmk1 regulating
during those processes? Well, we carried out
an RNA seek experiment, and what we found is that this pathway is regulating a whole variety
of fungal gene functions, including a raft of effector proteins. So about 59 temporally
co-regulated effector-like genes, which are regulated or
severe down-regulated in the absence of when we
inhibit the protein kinase with naphthyl PP1, and many
of these are known effectors. And what these effectors
are doing is actually suppressing plant defense. So clearly this pathway is responsible for suppressing plant defense responses, and particularly those at plasmodesmata, and we know, for example,
the callose deposition, and a number of other
things are being affected by the absence of this Pmk1 kinase. But in addition, there are a large number of other fungal proteins
which are being affected, and many of these are involved
in cellular morphogenesis. They’re involved in actin remodeling, they’re involved in the
repolarization pathways, they’re involved in the
regulation of hyphal constriction. And you can see that
process perhaps more vividly in this movie, you can see
that the fungus is actually undergoing a swelling at
the point of the junction, and then it will squeeze
through this narrower gap, and then move through the other side, and this is an actin binding
protein gelsolin GFP. So we can actually see an
accumulation of filamentous actin at that point, at this point
of hyphal constriction. And also, we have evidence
that this is actually another septin-mediated response,
there are septin collars which bound those hyphal constrictions, and septin mutants appear to be affected rather severely in their
ability to actually move from cell to cell, when we look at them in conditional views. So what you can see in
terms of Magnaporthe moving from plant cell to plant cell is some process which
are somewhat analogous to the process which occurred here during the early events of infection. The fungus is through
this MAP kinase cascade is able to regulate
effector gene expression to suppress host defenses,
particularly its cell junctions at plasmodesmata, but also
undergo cytoskeletal remodeling in order to generate a septin collar, and hyphal constriction,
actin-mediated hyphal constriction, in order for it to move
through pit field sites, and colonize the adjacent tissue. So what I hope that
illustrates is the fact that Magnaporthe has to undergo some really very elaborate morphogenesis, and a highly orchestrated
infection process from the very start, through
its whole infection cycle, right the way through
to symptom development. Okay, so finally then,
I just wanna tell you about some of the work we’re trying to do to do something more practical, and actually try and control this disease in the developing world,
and I’m gonna tell you about a project which
I’ve been taking part in, with a large number of collaborators, from two US universities,
Ohio State and Arkansas, and also a number of
institutes across Africa, in Burkina Faso, in Nairobi, through BecA-ILRI, and KARI, and also at the International
Rice Research Institute in the Philippines. And we’ve been trying
to undertake a project by which we can guide
plant breeding strategies for the control of rice blast. Rice blast is a hugely
important problem in Africa. Rice consumption has
increased dramatically, particularly in East Africa. Rice has always been eaten in West Africa for a much longer period of time, rice cultivation has a
longer history there. But rice consumption is increasing by about 12 to 15% per annum
in Kenya and in Tanzania, and it’s one of the most
popular food products, but that leads to importation of rice, because rice production is insufficient to actually deal with demand. And newly developed cultivars of rice, which are interspecific hybrids between Oryza glaberrima, African rice, and Oryza sativa, the
conventional Asiatic rice, lead to high yielding, locally adapted, somewhat drought-tolerant rice cultivars, but they are incredible
susceptible to rice blast disease. So rice blast disease is
actually the biggest single constraint on rice production now, really across the
Sub-Saharan African region. So what have we been doing? Well, Barbara talked about
these avirulence genes, which encode effectors,
so as you’ve heard, effectors are involved in the
suppression of plant immunity, but sometimes those effectors
can be recognized by immune receptors, which
are the products of major disease resistance genes in plants, and by understanding the
population structure, we can learn something
about the resistance genes which would be necessary to control the prevailing population of the fungus. So you can see, for instance, this rice blast isolate is
able to cause disease on a rice cultivar with
resistance gene Pi-50, but unable to cause disease
on Pi-2, and Pi-9, and Pi-ZT, which means it must have the
corresponding avirulence genes, the effectors which are
identified or recognized by that immune receptor,
and you’ll hear more about the molecular
mechanisms in the next talk, but if we can understand the prevailing rice blast population, it
should tell us something about the types of resistance genes which would provide durable
resistance in Africa. So what have we done? Well, what we’ve done is
collected around 1,000 rice blast isolates from a whole raft of different countries,
Kenya, Tanzania, Uganda, right the way across
Africa, and we’ve genotyped all of those, we’ve actually sequenced a significant number as
well, and we’ve pathotyped all of them against the
international differential sets, which is a near isogenic series of rice, differing by around 30 different
disease resistance genes. And we’ve, in that way, worked
out the prevailing Avr genes that are present in the
population, this gives you a type of data output
we get, so you can see, red would be disease, and green would be resistance,
so you can see that there are small numbers of cultivars
which are able to be resistant against a large number of different rice blast isolates from Africa. But if we put together that
data across all 1,000 isolates, and we’re collecting every year, we collect around 3 to
400 isolates per year, they’re GPS tagged, we
have a collection point in a bio-bank in Nairobi which
stores all those isolates, and then we back up those
storages in Arkansas, and in Exeter, and we have an ongoing disease surveillance process, particularly in Kenya,
Tanzania, and Burkina Faso, which is ongoing, and
happens on an annual basis. But what we can show so far is there are a group of race-specific R-genes, Pi-5, Pi-sh, Pi-2, Pi-1, Pi-9, and Pi-b, which will exclude the
overwhelming majority of the prevailing African
rice blast population. However, none of them singly
would be very durable, because the fungus is able to
overcome disease resistance so easily by mutation of these
effectors, these Avr genes. So, we have a process
by which we have ongoing pathogen surveillance,
we’re deploying those race-specific resistance
genes, but at the same time, we’re introgressing those in combination with non-race specific R-genes. So QTLs for rice blast tolerance, a susceptible resistance gene as a dominant susceptibility factor, which works by a different mechanism, and the number of different types of resistant loci which are
not non-race specific. And what we’re trying to do
is put together a combination of race-independent and
race-specific R-genes in order to produce a
stack of three to four dominant R-genes in combination with QTLs, and a susceptible R-gene as well, and do this in commercial, in widely-grown rice blast varieties. The way this process looks in the field, this is the type of work we’re
doing on an ongoing basis, particularly this is carried out, this is work in the Philippines at IRRI, but also mirrored,
we’re doing similar work in Burkina Faso where we’re testing QTLs for resistance, compared to a susceptible line, and this shows some of
our crossing populations. But to tell you about the work that we’re actually doing in both West
Africa and East Africa, so in West Africa, we’re
working on the most widely grown rice variety, Basmati 370, two NERICA lines, these are
the interspecific hybrid lines which are very susceptible. We’re testing a variety of
different resistance genes which have come through in our
pathogen surveillance system. We’re then introgressing those through marker-assisted breeding,
into these East African rice lines, and also
working with scientists at the Cote d’Ivoire in Africa rice, we’re introgressing them
into these two popular West African varieties
of rice, so we’ve started with Pi-9, but we’re stacking
two other resistance genes, and then the QTL, and a recessive resistance gene as well. So the process on an ongoing
basis will look like this. At the moment, we’re at the
point where we’re actually carrying out blast hot spot testing with some of the cultivars
that we’ve already generated, we already have our first cultivar which has got a subset of
those genes already in place, that’s being tested in blast hot spots, that are in nine different
countries across Africa, 24 different sites,
from Mali in the north, to Madagascar in the south. And we test those in those blast hot spots to see the durability of the cultivars that we’ve identified. We then do greenhouse
assessments, those are done in my lab, and also in
Arkansas, and in Ohio State. We have an ongoing process
by which we’re also looking for new resistance specificities, and then laboratory diagnosis to confirm the prevalence of known Avr
genes within that population. And in that way, our aim is, over the next three to four years, we hope that we’ll be in a
position to actually release, and go through product registration, and project registration,
we hope we’ll actually cultivar registration
would happen as early as the beginning of next year,
and those will be released to growers throughout that
region, and this is work which is funded by the Bill
and Melinda Gates Foundation, and BBSRC, our research council. Okay, so just to summarize the
things I’ve told you about. So what I hope that you’ve
learned from the first part of the talk, the developmental
aspects of the work, is that Magnaporthe’s infection
is a highly orchestrated and regulated process, strongly linked to cell cycle control,
and to the operation of specific signaling
pathways, which are able to perceive the external environment. Rice tissue invasion
similarly works in the same sort of way, where you’ve
got to regulate morphogenesis at the same time as regulating the suppression of host defenses. And finally, we’re developing the durable control strategy to try
and alleviate some of the problems that rice blast is causing in Sub-Saharan Africa. The work was done by a large
number of people in my lab, I won’t go through all
of them, but Lauren Ryder in particular was very
important in all of the work you’ve heard today on the turgor sensor, Wasin on the cell to cell
movement, Wasin Sakulkoo, and Mick Kershaw, and a number of others in terms of the applied work. Collaborators, well, both of the speakers, Sophien and Barbara are
major collaborators, in addition to a number
of our collaborators, particularly in that big African project. My lab is currently the
University of Exeter, but I’m very excited to be moving shortly to The Sainsbury Laboratory, to take on some new challenges, which is gonna be great fun. So, will answer questions
at the end of the session. Thanks.
(applause)