Phytohormonal and Transcriptomic Response of Hulless Barley Leaf in Response to Powdery Mildew Infection

Abstract

Powdery mildew (PM) caused by Blumeria graminis (DC.) Golovin ex Speer f. sp. hordei Marchal (Bgh) is one of the major yield reducing diseases in hulless barley (Hordeum vulgare L. var. nudum Hook. f.). Genotypes with contrasting resistance to PM offer unique opportunities to explore the transcriptome in order to understand the expression changes in genes and pathways. In this study, we explored the phytohormone levels and transcriptome of a Bgh susceptible (XL19) and resistant (ZYM1288) hulless barley genotypes at 0, 5, 12, 24, and 36 h post infection (hpi) with Bgh. We found relatively higher levels of abscisic acid, jasmonic acid, salicylic acid, and cytokinins in ZYM1288. The transcriptome analyses identified 31,354 genes that were enriched in signaling, energy, and defense related pathways. Higher numbers of differentially expressed genes (DEGs) were found in XL19 as compared to ZYM1288 after 5 (3603 vs. 2341) and 12 hpi (3530 vs. 2416). However, after 24 and 36 hpi, the number of DEGs was higher in ZYM1288 as compared to XL19 i.e., 3625 vs. 3034 and 5855 vs. 2725, respectively. Changes in hormone levels drove downstream expression changes in plant-hormone signaling that helped ZYM1288 to perform better under Bgh infection. The expression of DEGs in MAPK-signaling and Toll-like receptor signaling pathways, glucosinolate biosynthesis, glutathione metabolism, brassinosteroid metabolism, and energy related pathways indicated their common roles in defense against PM. Key genes related to PM-resistance were upregulated in the resistant genotype. These genes provide key information towards differences in both genotypes towards resistance to PM. The transcriptomic signatures explored in this study will broaden our understanding towards molecular regulation of resistance to PM in hulless barley.