Gene expression analysis of the powdery mildew infected awns of the wild wheat relative Aegilops umbellulata

The causal agent of cereal powdery mildew, Blumeria graminis, is an obligate biotroph that causes serious damages to cereal crop yields. In field environment, pustules of B. graminis first appear on leaves and stems of its host plant, and gradually increase the number of pustules from older to younger leaves, finally reaching spikes and awns. One accession of Aegilops umbellulata Zhuk., a diploid wild wheat relative, is naturally infected with native B. graminis spp. in the field environment of Kobe, Japan. We found that disease symptoms of the powdery mildew on awns of Ae. umbellulata were dramatically changed after flowering. In contrast to no visible pustules on awns before flowering, the powdery mildew fungi heavily sporulated after flowering. To dissect the molecular mechanism behind this drastic change, we tested gene expressions in awns of Ae. umbellulata before and after flowering by using RNA-sequencing. Compared with flag leaves, a large number of genes showed differential expression in the awns before and after flowering, suggesting that physiological change in the host cells induced the severe disease symptoms on the awns of Ae. umbellulata.