Rosie Bradshaw and Carl Mesarich’s 2020 lab group photo. From left to right, Silvia de la Rosa, Mercedes Rocafort, Ellie Bradley, Berit Hassing, Carl Mesarich, Rosie Bradshaw, Melissa Guo, Mariana Tarallo, Hannah McCarthy, Ashleigh Mosen (Photo supplied)
Murray Cox, Pierre De Wit, Carl Mesarich, Te Rōroa, Nari Williams, Rebecca McDougal, Beccy Ganley, students, postdocs and more . . . the many names of Professor Rosie Bradshaw’s research community punctuate the story of her career. As she recounts some of the highlights, she generously assigns credit to the people around her: the people who have inspired and motivated her to become an internationally celebrated plant pathologist.
When Rosie came to New Zealand in 1991 she was well acquainted with model organisms in healthcare, but hadn’t given much thought to pathogens in plants.
“Then I just happened to have a meeting with someone from Scion,” she says, “and they showed me a picture of a toxin from this forest pathogen, Dothistroma septosporum. It happened to be very similar to something I had worked on previously.
“It was mainly serendipity to be honest.”
From that first encounter with forest pathogens, Rosie started looking at the interactions between fungi and plants, and she never turned back.
She discovered the toxin, dothistromin, was a ‘virulence factor’, which means it’s one of the things the pathogen needs to successfully infect a plant and cause disease.
This disease, Dothistroma needle blight, was affecting pine trees around the world – threatening both economic values and ecological integrity.
“After the dothistromin discovery I was invited to join a research consortium with people from all around the world who applied to the Joint Genome Institute for genome sequencing. D. septosporum was selected to be one of 13 genomes they sequenced for free . . . that was at a time when sequencing was really expensive.”
Rosie was overjoyed at the selection, and receiving the completed genome was one of the most exciting moments of her career.
“The Institute did an amazing job of piecing the genome together to a chromosome level, which was a rare feat at the time.”
They soon realised that the D. septosporum genome was similar to that of a ‘famous’ tomato pathogen that had been used to understand how effector proteins work. The professor who pioneered this work didn’t take long to notice there was a new kid on the block.
Rosie says “I was invited to join a collaboration with Professor Pierre De Wit in the Netherlands, at Wageningen University. He’s a real hotshot – he’s like the father of modern plant pathology.
“I just couldn’t believe it. I couldn’t believe that I could collaborate with this great guy.”
The game-changing experience cemented her love of plant pathology. It also introduced Rosie to Carl Mesarich – then a postdoctoral fellow, now someone with whom she’s shared a Massey University lab for almost a decade.
Professor Rosie Bradshaw’s (right) legacy continues through her colleagues, like Dr Carl Mesarich (left) and her past and present students like, Taylah Dagg (middle).
Cracking the code to kauri dieback
Back in Aotearoa, Rosie joined the nationwide team who were collaborating to save a cultural treasure. But she’s quick to point out that she wasn’t there from the start.
“So my grandson actually told me a little while ago that I’m in Wikipedia,” she says, “which I didn’t know. It says that I identified kauri dieback but that’s untrue – I need to go fix that up!
“Prior to 2014 there was a relatively small group of scientists working on P. agathidicida (the pathogen that causes kauri dieback): Ross Beever (who did identify it), Nick Waipara, Stan Belgard, Bevan Weir, Ian Horner, among others. Nari Williams invited me to join the team just as awareness of kauri dieback really took off.”
Excited to be part of a “diverse, country-wide team” with a common goal, Rosie had never before worked on something with such cultural significance.
“Working on P.a. has given me a huge respect for Māori culture and makes me realise we’re all just doing a little bit of a bigger project. We’ve all got the same goal in mind, which is to try and save these trees.”
Rosie and her Bioprotection Aotearoa postdoc Mariana Tarallo are currently part of a team working closely with Northland iwi Te Rōroa. They’re using kauri leaves to help test their most promising lead.
Rosie says, “We’re working on a protein made by the pathogen (Phytophthora agathidicida) that suppresses or dampens down the defence responses the plant will put up.”
They’ve discovered the protein combats a broad range of plant defences. If they can knock out the production of this protein, it might enable the plant defences to overcome the pathogen and prevent infection.
“For example, we could use RNA silencing, that a lot of people are starting to use now. So spraying or injecting something into an infected tree that’s going to stop the pathogen from making its protein and from working.
“It’s a bit of a long shot because this pathogen is in a forest and it’s in roots, but people are starting to look at this sort of thing now with RNA silencing in forest trees, including root pathogens . . . so it’s looking hopeful.”
A long partnership with BA
Mariana is one of the latest in a long line of students and postdocs Rosie has mentored, with the help of Bioprotection Aotearoa (BA) and its predecessor the BioProtection Research Centre (BPRC).
She says both organisations have provided her teams with a continuity of funding that is unique and valuable, especially when other sources of funding have been scarce.
Rosie says “We have been unravelling some of the details about how the P. agathidicida pathogen interacts with its host; we sequenced the P. agathidicida genome (one of the first Phytophthora genomes in the world to be assembled to chromosome level); we have been looking at gene expression in kauri roots vs shoots; and our focus is now mainly on effector proteins, that help pathogens to invade their host.
“The BPRC and BA communities have really helped to drive forward collaborative and supportive connections between scientists from different organisations in New Zealand. Overall, the culture has been very supportive, welcoming and personalised.”
Where to from here?
Over the next few years Rosie will be busy writing manuscripts and wrapping up projects (except for a few that she’s only just started, of course!).
She says “I love gardening and walking, so I’d like to start spending more time in the outdoors and less at my computer! Plus, more time with my grandkids, and visiting family and friends.
“I’m also passionate about tree and forest ecosystem conservation so I really hope to get more involved in those areas.”
Rosie’s presence at her computer, in the lab or lecture theatre will be sorely missed when she starts reducing her hours, but her legacy in plant pathology will remain for generations to come. Thank you, Rosie, for adding some of your time and passion to the BA team!
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