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In planta comparative transcriptomics and Y2H to identify putative elicitors/suppressors of barley rpg4/Rpg5-mediated stem rust resistance

Roshan Sharma Poudel: Department of Plant Pathology, North Dakota State University

<div>The barley <em>rpg4/Rpg5-</em>mediated resistance locus (RMRL) confers resistance to many <em>Puccinia graminis</em> f. sp. <em>tritici</em> (<em>Pgt</em>) races, including TTKSK. <em>Rpg5</em> is the resistance gene at this locus encoding a typical NLR with a C-terminal protein kinase (PK) integrated sensory domain (ISD). To identify <em>Pgt</em> effectors/suppressors that elicit or suppress RMRL, 24 <em>Pgt</em> isolates with differential reactions were genotyped utilizing <em>in planta</em> RNAseq and 114K SNPs that result in predicted nonsynonymous amino acid changes were identified. Comparative analysis showed 17 genes associated with dominant RMRL virulence representing candidate suppressors of resistance. Host transcript analysis of a single barley line inoculated individually with the 24 virulent vs avirulent isolates showed virulent isolate specific down regulation of biotic stress responses, suggesting all <em>Pgt</em> isolates may contain a conserved effector that elicits RMRL responses by interacting with the Rpg5 ISD, yet virulent isolates harbor suppressors of resistance rather than the lack of a functional Avr protein. Y2H libraries constructed using RMRL avirulent isolate inoculated barley mRNA screened with the Rpg5 ISD as bait,identified a putative <em>Pgt</em> interactor that matches the criteria of a secreted effector and is highly expressed in all isolates. This suggests that it may represent the conserved effector that elicits Rpg5-mediated resistance responses. The validation of this putative effector and its function are underway.</div>

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