Peer review

Expansins are plant cell wall-loosening proteins that involve in response to environmental stimuli and various development processes. In this study, 1858 expansin members were identified in 40 plant species by using Hidden Markov Model profiles and searching against to rice and Arabidopsis expansins. They were classified into four groups: EXPA, EXPB, EXLA, and EXLB. The distribution of expansin genes in different plant species indicated that EXPA genes emerged first, and genes in EXPB, EXLA, and EXLB subgroups might be resulted from gene duplication. In wheat, there are 104 expansins, including 88 TaEXPAs, 8 TaEXPBs, and 8 TaEXLAs. Phylogenetic analysis showed that wheat, rice, and Arabidopsis expansins shared high bootstrap values, and the phylogenetic relationship of wheat expansins were supported by conserved motifs and gene structures. Evolutionary analysis of Triticum urartu, Triticum turgidum, and wheat expansin genes revealed that gene duplication, gene loss, and chromosomal rearrangement events occurred during the evolution process of wheat expansins. Three kinds of cis-elements, including development-related, hormones-related, and abiotic stress-related were identified in the promoters of wheat expansin genes. Meanwhile, the expression of wheat expansin genes is extensive and affected by abiotic stresses. Additionally, by overexpressing in Arabidopsis, the functions of TaEXPB1A in root and seed development were characterized. In combination with previous reports, these results indicated the extensive functions of wheat expansins. Shortly, this study identified wheat expansins more accurately, and extended the knowledge of expansin genes.

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