Genome-Wide Identification of the As2/LOB Gene Family in Elymus sibiricus and the Expression Profiles Characterization

Abstract Background The As2/LOB gene family plays critical roles in regulating plant growth, development, and abiotic stress responses. Despite this gene family has been characterized in multiple plant species, it remained unstudied in the perennial allotetraploid grass Elymus sibiricus , an important species for grassland restoration and forage production on the Qinghai-Tibet Plateau. Results We identified 64 As2/LOB genes in E. sibiricus and systematically characterized their chromosomal distribution, gene structure, conserved motifs, cis-acting elements, and phylogenetic relationships. Phylogenetic analysis classified these proteins into seven distinct subfamilies. Gene structure analysis revealed the presence of conserved domains and motifs characteristic of the As2/LOB family, underscoring both functional conservation and subfamily-specific divergence. Tissue-specific expression profiling across roots, stems, leaves, and spikes at multiple developmental stages revealed pronounced spatial and temporal patterns, with several subfamily members showing preferential enrichment in organs that directly determine plant architecture, nutrient acquisition, and photosynthetic capacity—key traits contributing to forage biomass and yield. In parallel, expression analysis under indole-3-acetic acid (IAA) treatment, a central phytohormone regulating organogenesis and cell elongation, further implicated these genes in auxin-mediated developmental networks underlying vegetative and reproductive growth. Promoter analysis identified numerous hormone-responsive and stress-responsive cis-acting elements, suggesting potential regulatory roles in hormone signalling and environmental adaptation. Chromosomal localization and synteny analysis indicated that the As2/LOB genes were unevenly distributed across the 14 chromosomes and identified multiple syntenic gene pairs, indicating that gene duplication events have contributed to family expansion. In addition, expression profiling under salt, drought, and ABA treatments revealed differential regulation of several members, suggesting their auxiliary roles in stress adaptation that may help stabilize biomass production under unfavorable environments. Conclusion This study provides the first comprehensive genomic resource for the As2/LOB gene family in E. sibiricus , revealing their expansion via duplications and functional diversification in organ development and biomass-related growth. Notably, EsLOB52 was consistently induced across IAA, salt, drought, and ABA treatments, highlighting its potential as a candidate integrator of growth regulation and stress adaptation. These findings establish a foundation for molecular breeding aimed at improving both biomass yield and stress resilience in E. sibiricus .