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Abstract

The barley rpg4/Rpg5 locus confers resistance against wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt) including race TTKSK (A.K.A. Ug99). The 70 kb region harbors two NLR R-genes, Rpg5 and HvRga1 that are required together for resistance. HvRga1 and Rpg5 contain typical NLR resistance-protein structure; however, Rpg5 has an additional C-terminal serine threonine protein kinase (STPK) domain. The transcription factor, HvVOZ1 was identified by yeast-two-hybrid of a library constructed from RNA of the rpg4/Rpg5+ line Q21861; 48 hours post inoculation, utilizing the Rpg5-STPK domain as bait. We hypothesize that the Rpg5-STPK acts as an integrated decoy that HvVOZ1 binds to negatively regulate defense activation or binds after activation as part of a signaling complex. The second NLR, HvRga1, may guard theHvVOZ1-Rpg5 interaction or surveil the Rpg5-STPK domain for Pgtrpg4/Rpg5-Avr (r45-Avr) effector manipulation. Thus, HvRga1 is possibly the guard that detects manipulation of the Rpg5 STPK or possibly HvVOZ1 by the r45-Avr effector eliciting a strong effector triggered immunity defense response. The r45-Avr needs to be identified to thoroughly investigate these mechanisms and test our hypothesis. To accomplish this a panel of 37 wheat stem rust isolates collected in North Dakota, many with differential race typing on the wheat differentials and differential reactions on rpg4/Rpg5 and Rpg1 in barley were genotyped using restriction site associated DNA-genotyping-by-sequencing (RAD-GBS). This RAD-GBS produced 4,919 informative SNPs and this initial genotyping was used to select 24 diverse isolates (16 avrRpg4/rpg5 and 8 Avrrpg4/Rpg5+) that were used to conduct in planta RNA-seq analysis during Pgt colonization 5 days post inoculation on the susceptible barley cultivar Harrington. The RNA-seq data was utilized to identify ~181,000 variant calls (SNPs and indels) within these Puccinia graminis transcriptomes during the infection process. The robust genotyping and phenotyping on these diverse differential isolates should allow us to identify candidate r45-Avr genes utilizing association mapping.

Biography

Robert Saxon Brueggeman has completed his PhD in 2009 from Washington State University and Postdoctoral studies also from Washington State University Department of Crop and Soil Science. He is currently an Associate Professor at North Dakota State University as the Barley Pathologist/Molecular Geneticist. He has published more than 32 papers in reputed journals covering the topics of the cloning and characterization of barley disease resistance genes and fungal effectors.

E-mail: Robert.Brueggeman@ndsu.edu