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August 29, 2025 19 mins

The Director of the Milner Centre for Evolution, Professor Turi King, talks to Dr Volkan Cevik, whose research focuses on understanding interactions between plants and their pathogens, as well as understanding how these pathogens evolve.

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(00:02):
Hello and welcome. You are listening to a podcast by the Miller Centre for Evolution at
the University of Bath. I'm Professor Turi King, your host, and today I'm talking to Volkan Cevik,
whose research focuses on understanding interactions between plants and their pathogens,
as well as understanding how these pathogens evolve. So, Volkan, how did you become

(00:27):
interested in how plants and their pathogens interact, was there defining moment for you?
Yes, there was. I was actually trained as a plant geneticist, my study was on apples,
and I was characterizing a specific phenotype in apples involving aphid resistance. And there

(00:47):
are only certain apple varieties that can actually confer resistance to this specific
aphid. And I was handling those individual aphids when it was inoculating apple leaves.
But at the end, if the apple varieties are susceptible, they develop this beautiful red
colouring on leaves. And the leaves basically curl in a way that aphids manipulate the apple leaves

(01:11):
to create its own house, like a shelter. Because the leaf curls and aphids actually go in there
and they basically, you know, live and reproduce.And I was really curious how on earth, you know,
aphids actually sort of imposed such, you know, kind of changes in a plant species. So,
everything started that way. but then few years later, with all this progress in plant field,

(01:36):
then we learned what's actually happening. Similar kind of things are happening during plant pathogen
interactions, plant insect interactions, plant nematode interactions. It's amazing.
So, there are common mechanisms involved in this, obviously the components are different,
but common mechanisms are involved in these processes in defining those interactions.

(01:56):
So Vulcan what kind of immune systems do plants have?
Obviously, the plants do not have like mobile cells like we do, like mammals. And they don't
have adaptive immune system, but they have sort of what they refer to as innate immune system.
Of course they have like physical system, you know, those trees have barks to protect themselves

(02:17):
or some plants actually have thorns. But in terms of innate immune system, they have like two layers
of immunity against invading pathogens or insects or other disease-causing organisms, I will say.
So, the first layer is very much effective against multiple pathogens. So, what they do
is they recognize what we call these highly conserved molecules. You know, for example,

(02:42):
what we know is in bacteria, you know, they need to swim. So how do they swim, they use flagella.
So basically, plants evolved receptor proteins recognizing a bit of that specific part of that
flagellum protein. That immune system is actually quite effective against multiple pathogens,
because don't forget there are multiple pathogens infecting multiple plant species at the same time,

(03:07):
but only certain pathogens are successfully infecting, only certain specific plant host
species. So, there is this beauty of this coevolution involved in this kind of process.
But then obviously some pathogens evolve to overcome that immune system. So, what they do
is there are certain proteins in the pathogens or insects or nematodes, they basically secrete those

(03:32):
proteins. And somehow some of those proteins find a way into the plant cell, inside the plant cell.
But then, of course, if the pathogen is successful in suppressing that initial immune response,
then some plant species actually evolved another layer of immune receptors or immune system. We
call it the second layer of immune system. So, this involves so-called resistant proteins. But

(03:59):
these are mainly inside the plant cell. So, it's like two, you know, layer of castle so,
you know, if the first wall is demolished and you have the stronger one. So, you just want to
protect yourself against all these invasions.So those proteins, then what they do is they
recognize those effector proteins which are actually translocated into the host plant

(04:22):
cell. If there is no resistant protein within that particular plant species, within the cell, then of
course, those effector proteins, they manipulate all sorts of different kind of processes, and
they basically convert the plant cell into a food factory for themselves. So, they can feed on them.
Obviously, it's all about specificity.Yeah.
It's all about coevolution because, you know, plants evolve resistant proteins against those

(04:46):
specific pathogens. So those resistant proteins then recognize those effector
proteins inside the host plant cell. And they then activate the second layer of
plant immune system which is unfortunately very strong. And that particular cell ends up dying.
Don't forget live plants do not have mobile cells, and mobile elements in that respect.

(05:09):
Yeah.Almost like
every single cell is able to resist itself against invading pathogens. So, what they do is all those
cells infected by the plant pathogen, they sort of undergo cell death, and they are actually able
to stop the pathogen. And that's a very strong response as opposed to the first layer, because

(05:29):
in the first layer of defence or resistance, plant cells are alive, but they produce compounds that
actually enable them to resist against pathogens.This interaction is very specific. For example,
we know that we have certain pathogens that can actually infect our roses, but they're not going
to go and infect cabbages and like Brussel sprouts and things like that. There is a specificity,

(05:52):
it’s all as a result of coevolution.Then what pathogens do they evolve as
well to avoid that recognition. So, they actually mutate their effective protein encoding genes,
and then that particular recognition disappears. And then what plants do
they evolve a new resistant protein.So, this goes on basically, I'm really

(06:15):
trying to understand that kind of mechanisms. What's actually happening was the diversity
in the field. And can we have an ultimate plant immune system that can actually be
very effective against multiple pathogens, you know, ensuring food security in future.
And that's basically what you're trying to understand, but you're trying to understand

(06:35):
it in particular species. You're looking at a particular pathogen, aren't you?
So, my work at the moment focuses on what we call this white rust pathogen. So white rust pathogen
infects what we call this Brassica species. Again, brassicas are, you know, everyday vegetables like,
you know, cabbages, cauliflower, Brussels sprouts, but also important oil crops like oilseed rape and

(07:01):
oilseed mustard and specially oilseed mustard is a one of the major vegetable oil crops in India.
Basically, I've been trying to understand the infection strategies by this particular
pathogen. And one thing I should mention here as well, white rust pathogen, it was actually
considered to be a fungal pathogen, but it's not. It's actually another group of pathogens

(07:24):
we call oomycetes. And it is actually related to potato late blight pathogen. That's the
pathogen which caused the Irish famine.I mean that goes into it quite nicely,
what does white rust do to the plant.Yeah.
So, if it's very similar to this one that caused the potato famine, I'm guessing what
it does is it really damages the plant.Yeah. It doesn't cause such a damage

(07:49):
like the potato blight. One of the things that we discovered throughout my studies,
as well as my colleagues work, it's an amazing immune suppressant. So basically,
once it infects the host plant, it suppresses its immunity really effectively. So, if another
pathogen come along which will normally never infect that plant, starts infecting the plant.

(08:12):
So, it's like it opens the door for other pathogens to get in.
Exactly. But of course, any infection will lead to reduction in photosynthesis. We know in plants
that's how we produce sugars. And you know how everything actually, you know, is dependent
on. You know, that's one of the most important aspects of being a plant is the photosynthesis.

(08:33):
It will basically massively impact the yield.But sometimes white rust can be systemic.
What I mean by systemic is, it infects, let's say through the leaf and it goes through all the,
you know, vascular system. And then it actually colonizes the entire plant. But then what it
does is after it completes its life cycle, it produces millions of spores. And those spores

(08:57):
will be either through water splashes or wind, they will be traveling quite a long distance,
and it can actually infect other plants within the field or nearby field or, you know, further away.
So, tell me, how does the white rust work? Because that's what you're interested in
looking at isn’t it?Yes.
You're trying to understand what's the interaction between this pathogen and this plant, basically

(09:21):
how the pathogen is getting in, I'm guessing.Yeah.
So, tell me about that.So, white rust they produce
these structures called zoospores, a bit like bacteria that has got flagella as well,
so it can swim. It requires water basically to infect. So, these are sort of like water dwelling
organisms. They were actually considered to be fungus in the past because of how they look. But

(09:42):
they're not actually they're totally different.And they actually form these zoospores,
and they swim. And they actually, this particular pathogen I work on enters through stomata. And
then those zoospores like seeds, you know, they started germinating, in this case obviously
zoospore will form what we call these hyphae. These are the extending structures of what

(10:03):
we call these filamentous pathogens. So that enables them to squeeze in those plant cells,
inside the plant leaf and colonize the leaf.But what is exciting is, they form these
structures, what we call this haustoria. So, these are attached to the pathogen, you know,
hyphal body, and they basically engulf into the plant cell. So, they push the plant cell,

(10:29):
engulf into the plant cell. And they basically suck all the nutrients from the plant cell. Yeah.
But of course, before doing so, as I said, they secrete and translocate those proteins,
they go into the plant cell, they manipulate the whole plant cell and they become like,
feeding factories for this particular pathogen.So of course, one of the major aspects of plant

(10:54):
cell is those cells are photosynthetic cells. You know, they're active in terms of photosynthesis.
They produce a lot of sugars. So, what you want to do as a pathogen, maybe you just get
all this sugar. You know, you don't want to share too much with the plant itself.
But of course, this particular pathogen is quite exciting because at the same time, it can actually
sort of systemically immune suppress. So, what it does is, you know, it infects a part of the leaf,

(11:20):
let's say one part, but the entire leaf becomes immunosuppressed. So even the non-infected part
can now be infected by other pathogens as well. You know, just to make sure that plant
has no resistance at all, basically.So, it's really taking over the plant.
Yeah.Not even just
where it's invading, but around it as well. So, this is all about food security, there

(11:42):
is a direct application for your research because…Yeah, from evolution all the way to food security.
Yeah.Absolutely.
Yeah.Absolutely.
Because eventually what you want to do is presumably be doing that for crops here,
but as you say, you're already helping people in India. And so
are the main crops that you're working on brassicas or are you
starting to move into any other ones or…I also started working on plant viruses. I

(12:04):
have collaborators in Türkiye and Akdeniz University in Antalya, and that's one of
the major areas where they grow glasshouse tomatoes and peppers and, you know, vegetables.
So, during our conversations they told me almost all the tomato varieties were infected by two

(12:25):
diverse plant viruses. But what was fascinating is one of them, its genome encodes 4 proteins maximum
and is threatening the world tomato production right at the moment. And it's amazing, you know,
how do you achieve that? How do you do this?Okay. So, let's back up a little bit. Viruses

(12:46):
what they do is they get into a cell; they take over the cell…
Absolutely…Just to copy themselves and move on…
And then move from one cell to another. And then they actually reach the vascular system and then
they just move within the entire plant.Okay. So, what are you doing to
preserve the world's tomatoes then?There are, of course, certain chemicals
you can use, you know, to kill viruses, but in an agricultural context, we are very much dependent

(13:12):
on plant genetics, host plant resistance.So, basically what you need to do is,
you develop new resistant varieties. That's pretty much to my understanding the only the way
that we can actually deal with them.Exactly. And the thing is, is we have an
adaptive immune system so we can get vaccines, our body goes, oh, that's a virus. I will make

(13:33):
something against that virus, and I will get rid of it. But you can't do that with plants.
No.So, you are basically stuck,
as in you need to have varieties that are automatically immune to some extent or where
you do genetic modification, presumably…Absolutely, absolutely.
Where you give them that immunity.That immunity. Yes, exactly. But the
problem with viruses is, you develop a new variety, you know, you just spent years to

(13:59):
develop that variety, and then you put them in the field and within a year, it's no longer
resistant to virus. Because virus evolves so quickly, you know, they've got this variance.
I'm actually doing a different approach. In my lab, what we try to do is, you know,
as I mentioned, for example, in this particular of the virus,
it's got 4 proteins maximum. But we're actually focusing on two of those proteins and what they

(14:24):
do in the plant. And what sort of plant proteins they actually target, what sort of pathways they
actually manipulate to make plants become a virus replication factory, basically.
So, is that a way of attacking it? So, stopping the virus from even getting into any of the cells,

(14:44):
or is there no way you can do that? You just basically have to give the plants some
sort of immune system once they get in?Virus will find a way because, you know,
damages and things like that, you know, there will be a way for virus to somehow enter the
plants. You know, just one single plant cell is enough as long as it can enter into one of them.
Yeah.But then what
we can do is we can find some new mechanisms to stop virus moving from one cell to another.

(15:10):
Oh, okay.Or we can actually stop
virus to go into the vascular system and to move within the plant. So that's what I'm trying to
understand now. So, what were you doing is we are actually finding which plant proteins mediating
that. It's like an Achilles heel basically. You know, there are certain host proteins,

(15:31):
what makes us susceptible, for example. What makes humans or animals or plants susceptible to other
pathogens because don't forget those enemies, pathogens or viruses, they take advantage of your
own protein or your component within yourself.So, this is what we try to identify. So,

(15:51):
what sort of host proteins are somehow manipulated by the virus protein, and which makes this virus
to move, replicate etc... And then what is beautiful about this system is, if we can
identify 1 or 2 of these proteins and we can actually edit, using genome editing technologies,

(16:12):
those genes encoding those proteins, and then we will have transgene free plants.
So, the plants presumably need the proteins. But if you can edit them in such a way that
it stops the virus, but the plant is still happy.Yes, exactly. I mean, there are some really good
examples as well. So obviously some of those proteins are essential for plants,

(16:33):
there's not much you can do with it. This is why the work get a bit complex in a way,
but we can mutate some of those genes, but the protein might still be there, might be doing its
function in a way or some of them actually just, you know, we don't necessarily see a
massive detrimental effect in the plant life, but the plants will be resistant to the virus.

(16:57):
So what technologies are you using, are you using Crispr?
Crispr Cas9 technology. And what is beautiful about that is you edit maybe a single nucleotide
in DNA and remove all the components, and you basically end up with a variety almost
identical to the variety you start with, with a single base pair difference. So, in a way that

(17:19):
is really effective, and it will take a long time for the pathogen in general to gain something new,
to be able to actually infect that particular plant species. Again, evolution in action really,
it’s the beauty of evolution in that respect.What's the ultimate goal of your research? What
would make you happy if you get to the end of your career and you look back and you go, I did that.

(17:44):
It's not actually easy question to answer, but for me, if I can see the work that I did with
my colleagues in India, if I can see some of those farmers who can’t spray their plants with
pesticides or fungicides, can grow some of those varieties that I'm involved in developing, I think
I will be more than happy because that means I actually did contribute to global food security.

(18:10):
You know, thinking about the future with the climate change, I mean,
climate change will impact the region where half of the population lives today, you know, those are
the people who already actually, sort of, need support for security. But of course, some of my
findings are being used by the next generation, that will make me extremely proud as well.

(18:33):
Volkan, thank you so much for talking with me.This was a podcast by the Milner Centre for
Evolution at the University of Bath. I'm Turi King and thank you for listening. If you have
any thoughts or comments on this or any other episodes, please contact us through social media.
For more information about the Milner Centre for Evolution, you can visit our website.
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