Genome-wide identification of expansin gene family in barley and drought-related expansins identification based on RNA-seq

Expansins are cell wall loosening proteins and involved in various developmental processes and abiotic stress. No systematic research, however, has been conducted on expansin genes family in barley. A total of 46 expansins were identified and could be classified into three subfamilies in Hordeum vulgare: HvEXPA, HvEXPB, and HvEXLA. All expansin proteins contained two conserved domains: DPBB_1 and Pollen_allerg_1. Expansins, in the same subfamily, share similar motifs composition and exon-intron organization; but greater differences were found among different subfamilies. Expansins are distributed unevenly on 7 barley chromosomes; tandem duplicates, including the collinear tandem array, contribute to the forming of the expansin genes family in barley with few whole-genome duplication events. Most HvEXPAs mainly expressed in embryonic and root tissues. HvEXPBs and HvEXLAs showed different expression patterns in 16 tissues during different developmental stages. In response to water deficit, expansins in wild barley were more sensitive than that in cultivated barley; the expressions of HvEXPB5 and HvEXPB6 were significantly induced in wild barley under drought stress. Our study provides a comprehensive and systematic analysis of the barley expansin genes in genome-wide level. This information will lay a solid foundation for further functional exploration of expansin genes in plant development and drought stress tolerance.