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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SPLINTER (Signaling of plant intracellular immune receptors)

Teaser

Summary

Plant diseases are an economic, environmental and social threat affecting crop production worldwide. Deployment of resistance (R) genes in crops is currently the most effective strategy for genetic control of disease. However, genetic resistance mediated by R genes can be short-lived and is often affected by environmental stresses such as elevated temperature, which is highly concerning in the context of global climate change. The provision of durable and effective disease resistance is imperative for the protection of the environment and a global food security perspective. Thus, better understanding plant immunity is crucial to improve or develop novel disease resistance management plan adapted to predicted climate change.
The plant immune system is based on a combination of cell surface and intracellular receptors that recognize various infection-associated molecules. Many disease resistance (R) genes encode intracellular receptors that specifically detect effectors delivered inside the host cell. Intracellular immune receptors belong to a large family of nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs), which are related to some innate immune receptors in animals. The opportunity at the heart of this project arises from the finding that N-terminal domains of NLRs act as potent signaling domains that are self-sufficient to activate immune responses independently of pathogen recognition. I found that immune signalling induced by isolated N-terminal domains is not affected at elevated temperature, unlike full length NLRs, suggesting that manipulating signalling downstream of NLR activation may provide a source of resistance that is tolerant to temperature stress. Naturally occurring truncated NLRs lacking some of the canonical domains but containing the N-terminal signalling domains are promising candidates to investigate this hypothesis.
The overall objective of SPLINTER is to decipher the signalling mechanisms of canonical and naturally occuring truncated NLRs under biotic and temperature stresses. This research focus on the functional analysis and natural variability of canonical and non-canonical immune receptors by using the the model plant Arabidopsis and the major vegetable crop tomato, mainly in response to the devastating phytopathogenic bacteria Ralstonia solanacearum.
It has three specific aims to study the following questions:
1. What are the very first steps following canonical NLR signaling activation? (aim1)
2. What is the role of truncated NLRs in disease resistance? (aim2)
3. Can truncated NLRs or signaling partners confer disease resistance in the context of climate change in tomato? (aim3)

Work performed

Due to pregnancy, I had to suspend SPLINTER four months after its commencement.
1.During the first four months, I initiated the characterization of a promissing signalling protein candidate that interacts with several N-terminal signalling domains from different NLRs (protein-protein interaction validation and reverse genetic). This finding allowed me to develop a new collaboration in France.
2. Upon exploration of available transcriptomic data, I observed that several truncated NLR genes are upregulated upon R. solanacearum infection in Arabidopsis, suggesting that these proteins may play a role in Arabidopsis immunity in response to Ralstonia.
3. Before SPLINTER started, I have shown that immune signalling induced by isolated N-terminal domain from two different NLRs from Arabidopsis and flax, is not inhibited by an elevation of temperature. During SPLINTER, I have extended this finding by showing that signalling induced by another type of signalling domain present in wheat NLRs is also tolerant to elevated temperature, hence supporting that temperature stress tolerance of immune response dowstream of NLR activation is a general mechanism including in crops.
During this short period I established my research network in France. This includes participating to and presenting my project at the first Toul-effectome meeting, a local network of scientists working on microbe effectors and plant immunity. I also attended seminars series of the host institute and presented at weekly group meeting of the Deslandesâ€™ group, which allowed me to interact and exchange with my peers on a regular basis. I was also contacted by a coordinator of Â« pint of science Â» Toulouse to present my work to the general public (planned in May 2019)

Final results

NLRs are key component of the plant immune system. However, NLR-mediated immunity is often affected at elevated temperature, which is highly concerning in the context of global warming. One fundamental question in NLR biology is how these receptors activate signaling pathways to provide disease resistance. Given the global climate crisis, better understanding NLR function and signaling under temperature stress is a research area of major importance but is still poorly understood. This research is expected to not only uncover yet undescribed immune signalling mechanisms and considerably enhance our knowledge of plant immunity, it also has a great potential to provide crucial clues to develop new disease resistance methods adapted to global changes.
Although SPLINTER only lasted four months, it was a real stepping stone for my research career to transition from my position in Australia to reach and independent and permanent research position in France. Indeed, I secured a permanent research position and I have now fully established my research in France. During SPLINTER I was also selected for an interview to obtain an ERC starting grant. I obtained helpful advice and feedback from my peers at LIPM and received a specific training to prepare for this interview.