Papilla formation, defense gene expression and HR contribute to the powdery mildew resistance of the novel wheat line L699 carrying Pm40 gene

Abstract

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive wheat diseases worldwide and causes severe yield losses in most wheat-growing areas. POWDERY MILDEW (Pm) genes are responsible for wheat resistance to Bgt. Recently, a wheat line L699 carrying a novel Pm40 gene which was originated from Elytrigia inermedium, was developed and showed high resistance to Bgt; however, the resistance mechanism of L699 is still unclear. In current study, a range of defense responses were examined in wheat line L699 inoculated with Bgt, using a highly susceptible cultivar CN26 without Pm40 gene as a control. We found that high levels of reactive oxygen species (ROS) were rapidly accumulated and abundant papilla were formed at the infection sites where Bgt conidiospores germinated with abnormal morphology at a high frequency on L699 compared to CN26. Local hypersensitive cell death and defense genes in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways were then rapidly induced in L699. As a consequence, L699 exhibited no typical disease symptoms, whereas CN26 were fully covered by white hyphae and conidia. These data provide evidence that for the resistance of the wheat line L699 with the dominant gene Pm40 against Bgt, early ROS accumulation and papilla formation acts as dominant penetration resistance, leading to morphological abnormality of Bgt, when defense gene expression in SA and JA signaling and HR response enhance the post-penetration resistance by arresting onset of Bgt.