Characterization of molecular mechanisms regulating RPM1 protein function and localization
Final Report Abstract
Plants evolved a very sophisticated, two-tiered immune system to detect and fight pathogens. Intracellular resistance (R) proteins of the NLR family play a major role in the recognition of effector (Avr) proteins, injected into the plant cell by various microbes. NLRs sense the presence of effectors either directly or indirectly by monitoring effector-induced modifications on host proteins. This leads to NLR activation and eventually the induction of an effector-triggered immunity (ETI). The mechanisms of NLR activation and downstream ETI signaling are not well understood. This project aimed to analyze mechanisms regulating NLR activation and function, using the Arabidopsis NLR protein RPM1. RPM1 is activated by sensing the effector-induced increase of phosphorylation of a specific residue on the small plasma membrane localized host protein RIN4. To determine whether RPM1 activation is facilitated via a charge interaction with the phosphorylated (negatively charged) RIN4 we substituted positively charged residues of the RIN4-interacting domain of RPM1 with alanines and screened for loss-of-activation mutants. Our results indicate that at least three residues may have a function in sensing the phosphorylation on RIN4 and are important for RPM1 function. Unexpectedly, we were also able to isolated three gain-of-function mutants rendering RPM1 auto-active. Intramolecular interaction analysis of RPM1 domains containing these mutations suggest a model in which the coiled-coil domain is involved in regulating the conformational change of the nucleotide-binding domain to allow nucleotide exchange in the activation process. We are now examining if this is translatable to other plant NLR proteins. In addition, I was able to start two successful collaborations during the funding period that resulted in two publications in internationally well-recognized scientific journals. The results obtained in this work demonstrate a role of the retromer complex in immunity associated cell death in Arabidopsis, and illustrates how structural elements regulate the auto-activity of a maize NLR protein.
Publications
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A Plant Phosphoswitch Platform Repeatedly Targeted by Type III Effector Proteins Regulates the Output of Both Tiers of Plant Immune Receptors. Cell Host and Microbe 2014 Oct 8;16 (4):484-94
Chung E, El Kasmi F, He Y, Loehr A, Dangl JL
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Molecular and Functional Analyses of a Maize Autoactive NB-LRR Protein Identify Precise Structural Requirements for Activity. PLoS Pathog. 2015; 11 (2): e1004674
ang GF, Ji J, El Kasmi F, Dangl L. J, Johal G, Balint-Kurti P
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Retromer Contributes to Immunity Associated Cell Death in Arabidopsis. Plant Cell 2015; 27 (2): 463-79
Munch D, The OK, Gro Malinovsky F, Liu Q, Vetukuri RR, El Kasmi F, Brodersen P, Hara- Nishimura I, Dangl JL, Petersen M, Mundy J and Hofius D
