Transcriptional Profiling and Genetic Mapping of Barley Responses to Bacterial Flagellin.

Diverse plant species detect bacterial flagellin using leucine-rich repeat receptor-like kinases (LRR RLKs) to activate defense responses and promote resistance against bacterial invasion. In barley, the impact of flagellin on inducible defense responses has not been fully described. Here, we report that the flagellin-derived flg22 peptide induces callose, ROS bursts and differential expression of 2603 genes in barley. Cultivated barley genotypes produce different amplitudes of flg22-induced ROS bursts indicating genetic variation for MAMP responses. Association mapping revealed a region on chromosome 7 underlying variation in flg22-induced ROS bursts, which contains 12 flg22-induced genes. Genotypes with higher flg22 responses had higher induced resistance to pv. (), the causal organism of bacterial leaf streak. The flg22 region of flagellin evades detection in both barley and Arabidopsis, and a single amino acid change can restore immunogenicity of the peptide. Together, this work underlines the effectiveness of the flagellin-triggered defenses in promoting barley resistance to which evades recognition of the flg22 region in its host.