Identification of the AVRa7,AVRa9, AVRa10 and AVRa22 effector genes from barley powdery mildew fungus (Bgh) association analysis between transcript polymorphisms and AVRa phenotypes from 27 Bgh isolates.

Disease resistance is mediated by specific recognition of pathogen avriulence effectors (AVR) by nucleotide-binding leucine-rich repeat (NLR) receptors. The barley (Hordeum vulgare) mildew locus A (mla) resistance gene homolog 1 (RGH1) encoded NLRs (MLAs) confer isolate-specific resistance to the widespread mildew fungus Blumeria graminis forma specialis hordei (Bgh). In barley, MLA has been subject to extensive functional diversification, resulting in allelic resistance specificities, each recognizing a cognate Bgh AVRa. The by genetic association isolated AVRa1 and AVRa13 effectors belong to the candidate secreted effector protein (CSEP) gene family (Lu et al., 2016). To unravel the complex mechanisms underlying MLA functional diversification in barley and wheat, isolation of numerous Bgh AVRa genes and recognition of their gene products by MLA is necessary. Our here deployed higher resolution genetic association approach identified the Bgh avirulence gene candidate loci AVRa7, AVRa9, AVRa22 and AVRa10 by associating of transcript polymorphisms and AVRa phenotypes from a collection of 27 Bgh isolates. We collected 10 Bgh isolates from a local Bgh population in Cologne in addition to our previous collection of 17 Bgh isolates (Lu et al., 2016). Overall design: Detached leaves of the barely cultivar Pallas or Manchuria were infected with previously sequenced Bgh isolates CC52 and CC88 (Lu et al. 2016, PNAS) as well as 10 new Bgh isolates collected locally in Cologne in 2016 and 2017. For each isolate, samples were collected at 18 and 48 hours post inoculation (hpi), and RNA extracted as described below, resulting in a total of 32 RNA-seq samples that were analyzed.