PS Webinar Series: Co-evolutionary diversification of barley MLA immune receptors by sequence-unrelated powdery mildew AVRA effectors

Abstract - Disease resistance is mediated by recognition of pathogen avriulence effectors (AVR) through host nucleotide-binding leucine-rich repeat receptors (NLR). The barley (Hordeum vulgare) mildew locus A (mla) 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 at their LRR domains, resulting in allelic resistance specificities, each recognizing a cognate Bgh AVRa. The isolated Bgh AVRa1, AVRa7, AVRa9, AVRa13, AVRa10,and AVRa22, which encode small secreted proteins recognized by allelic barley MLA1, MLA7, MLA9, MLA13, MLA10, and MLA22 receptors, respectively. AVRA effectors induce MLA-specific cell death in barley, Arabidopsis thaliana and Nicotiana benthamiana. The isolated AVRa effectors are sequence-unrelated, except for allelic AVRa10 and AVRa22 that are co-maintained in pathogen populations in the form of a balanced polymorphism. Co-expression experiments with matching Mla-AVRa pairs indicate direct detection of fungal effectors by allelic MLA receptors, although the effectors have not (recently) diversified from each other and that protein regions of AVRA effectors recognised by the matching MLA receptors differ between these sequence-related and unrelated effectors.

Biography - Isabel received a BSc and engineering degree from the University of Applied Sciences in Esslingen am Neckar, Germany. During her undergraduate studies, she visited the Research School of Biology, ANU to work under the supervision of Nijat Imin, on ‘cold induced anther protein in rice’ and ‘CLE peptides involved in the regulation of nodulation in Medicago trancatula’. Isabel’s PhD work in the group of John Rathjen focused on the regulation of plant immune receptors. Her postdoctoral studies at the Max Planck Institute for Plant Breeding Research, Cologne, Germany characterise Blumeria graminis effectors recognized by barley MLA NLRs.