ELUCIDATING THE ROLE OF SMALL PEPTIDES IN FACILITATING BACTERIAL INFECTION OF RICE

TheXanthomonas oryzaepv.oryzaesecreted peptide, RaxX, can be detected by the rice immune receptor XA21 leading to activation of defense responses againstXoo. However, details of this immune signaling pathway are still unclear. Interestingly, RaxX shares many similarities with the endogenous plant PSY peptides. But we do not know what RaxX is targeting to facilitateXooinfection in rice plants lacking the XA21 immune receptor. The overall aim of this research project is to better understand how plants perceive plant (PSY) and microbe (RaxX) derived peptides through leucine-rice repeat receptor-like kinases (LRR-RLKs), with the end goal of improving rice disease resistance. Results of this research will provide new strategies to engineer plant receptors, expanding disease resistance options available to plant breeders. To reach this goal, we will complete the following objectives:Objective 1: Identify and validate functional interactors of the XA21 immune receptor.The goal of this objective is to identify signaling components involved in XA21-mediated immunity following RaxX recognition. To identify novel protein interactors important for XA21-mediated immune signaling in rice, I will use the proteomics approach: TurboID proximity labeling. After identifying XA21-mediated immune signaling partners I will create CRISPR-edited lines in these genes of interest. To validate if these identified XA21 protein interactors affect XA21-mediated immunity againstXooinfection, I will conductXoodisease assays with the aforementioned CRISPR-edited lines. Changes in host resistance will be measured by bacterial counts and lesion length measurements.Objective 2:Identify the PSY receptor that binds both the RaxX and PSY peptides in rice and Arabidopsis.The goal of this objective is to identify the PSY receptor(s) to better understand PSY signaling and perception, in an attempt to determine how this pathway contributes to increased susceptibility of rice toXooinfection. I hypothesize that RaxX is targeting the PSY receptor to facilitate infection, based on the similarities between the RaxX and PSY peptides. First, I will test PSY receptor candidates in rice using the Ronald Lab's fast neutron mutagenized rice population. Second, I will generate high order knockouts in PSY receptor candidates in Arabidopsis. Rice and Arabidopsis PSY receptor candidate mutant lines will be screened for a response to RaxX and PSY peptide treatment through root growth assays.The results of this work will improve our understanding of the role small, sulfated peptides play in plant-microbe interactions allowing us to improve breeding efforts to create more disease resistant crops. Understanding how (1) plants recognize pathogen secreted peptides to initiate defense responses and (2) how pathogens hijack host developmental signaling pathways to cause disease will allow us to improve breeding efforts to create disease resistant crops. These objectives will be completed by a full-time postdoctoral scholar (2.0 FTE for the 2-year project duration) and a hired part-time undergraduate student for two quarters each year (0.4FTE for the 2-year project duration).