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.
Highlights
Hulless barley (Hordeum vulgare L. var. nudum Hook. f.) is an important cereal and used in human food, animal feed, and malt products
The methyl Jasmonate (MEJA) levels in Xila 19 (XL19) remained more or less constant but in the resistant genotype, the level increased with time until 24 hpi as compared to 0 hpi (Figure 2ix)
It is to be noted that ZYM1288 had higher tZ levels as compared to its control, while in case of XL19, a significant rise was observed at 5 hpi and the levels decreased unit 24 hpi and after 36 hpi, the levels were lower than 0 hpi
Summary
Hulless barley (Hordeum vulgare L. var. nudum Hook. f.) is an important cereal and used in human food, animal feed, and malt products. It has been reported that PM causes reduction in 1000-kernel weight, crude protein content, and yield in monocots such as winter wheat and barley [4,5]. Bgh has characteristics such as a repertoire of Avr genes, asexual haploid spores, and genetic recombination ability during the growing season, which support its rapid evolution [6]. Recessive mutations Mlo gene(s) confer durable resistance to Bgh, these genes are associated with pleotropic effects and exhibit spontaneous necrosis leading to loss of photosynthetic area and yield [14]. Other modulators of the innate immune response in plants such as CYP79B2, CYP79B3, WRKY21, suppressor of the G2 allele of skp (SGT1), S-phase kinase-associated protein 1 (SKP1), molecular chaperones (HSP90), RPM genes, and other resistance related genes i.e., disease resistance gene analogs (RGAs) have been implicated in defense responses against PM [15,16,17]
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