Dr Mariana Tarallo, a postdoctoral fellow at Massey University
Just like humans, plants have immune systems with sophisticated ways to recognise and defend against diseases. What if we could manipulate this system to stop the spread of diseases like kauri dieback disease (Phytophthora agathidicida) that threaten Aotearoa New Zealand’s native plants and ecosystems?
Mariana Tarallo, a postdoctoral researcher working with Professor Rosie Bradshaw and Dr Carl Mesarich at Massey University, is in the early stages of molecular research that hopes to identify a type of protein in the kauri dieback pathogen called a ‘virulence effector’. These effectors help a pathogen infect the host plant, although they can also be recognised by proteins in the host plant to trigger an immune response. Scientists hope they can one day stop the spread of the disease by “turning off” the production of these effector proteins, and/or by identifying the host proteins involved in the plant’s defence response.
Mariana’s work relies on previous research that has sequenced the whole genome of the kauri dieback pathogen, giving her lots of information about how to identify these virulence effector proteins. However, understanding its effects on the host is more complex, because kauri is one of the largest tree species in the world.
She is therefore using an exotic, fast-growing model plant (Nicotiana benthamiana) to try to identify the proteins, with the hopes of one day transferring the experiments to native hosts to identify resistance genes.
Performing lab tests on a model plant the fast growing model plant, Nicotiana benthamiana
Working with the James Hutton Institute in Dundee, Scotland, Mariana has found a way to identify the pathogen and plant proteins interacting with each other by using a known protein “library”. She has identified a potential target protein in the model plant which is highly “conserved”, meaning that it may also be present in many plant species, perhaps even trees like kauri. She is now planning on using a protein library for pine trees, which are more closely related to kauri, to see if she can locate the same host protein.
On the pathogen side, she plans on using a technique called RNA interference (RNAi), which uses a “silencing mechanism” in the form of a double-stranded RNA fragment to “turn off” the gene producing the effector protein. The RNA fragments are sprayed onto the infected plant, preventing the pathogen from producing the effector proteins and therefore stopping or reducing the spread of the disease.
While this is a hopeful start, Mariana explains that, “At this stage, it is more about understanding what the pathogen secretes to make it possible to infect the host and how the pathogen might be suppressing the host immune system. The more we understand, the more we can help, but this will be a long process.”
The system is complex with lots of target proteins, each of which can recognise more than one pathogen protein. Moreover, even if researchers can find the right host proteins to trigger an immune response, they will still need to make sure the pathogen doesn’t just evolve in response and become resistant to the plant’s defences. Nonetheless, the research team’s fundamental science is critical to our ability to eventually protect native plants from this disease.
Working in Aotearoa New Zealand has been a unique experience for Mariana, who is from Brazil. She says, “When I got here, I found it very different to what I was used to seeing at home. Funding research to understand, at the molecular level, a problem for a native species – unfortunately I don’t see this often in Brazil – and I find it very nice that Bioprotection Aotearoa is concerned about native species that are important.”
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Every detail in Mariana’s research, from the smallest discovery to the most intricate analysis, adds depth to the unfolding story. There’s still more to uncover.
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