Gene expression study for barley powdery mildew susceptible cultivar (cv) Baudin near-isogenic lines (NILs) introgressed with mlo-11 and mlo-11 (cnv2) mutations and cv Palace NILs with and without the mlo-5 null mutation.. Barley RNA sequencing of Mlo near-isogenic lines

Wild barley accessions have evolved broad-spectrum defence against barley powdery mildew through naturally occurring recessive mlo mutations. However, mounting the mlo defence response is associated with deleterious phenotypes with a cost to yield and fertility, with implications for natural fitness and agricultural productivity. This research elucidates the mechanism behind a novel mlo allele, designated mlo-11 (cnv2), which has a milder phenotype compared to normal mlo-11. mlo-11 (cnv2) appears to mitigate the physiological effects of mlo while still endorsing a high level of powdery mildew resistance. RNAseq showed this is achieved through partly restricted expression of Mlo, allowing adequate temporal induction of defence genes during infection and expression close to wild-type Mlo levels in the absence of infection. Gene ontology of mlo-related genes expressed during infection showed enrichment for amino acid and aromatic compound biosynthesis, together with stress, defence and innate immune responses. Examination of highly expressed genes revealed a new transcription binding motif (consensus ACCCGGGACTAAAGG), that appears central to mlo resistance and which is present in two WRKY transcription factors.