Integrated transcriptomic and metabolomic profiling reveals genotypic differences in UV-B radiation tolerance mechanisms in Elymus sibiricus L.

Ultraviolet-B (UV-B) radiation in the Qinghai-Tibet Plateau (QTP) is a crucial environmental constraint affecting plant distribution and development. E . sibiricus is an important perennial grass species used for pasture establishment and grassland restoration in the QTP, whose molecular adaptation to UV-B stress remains underexplored. Herein, phenotypic physiology, transcriptomics, and metabolomics were integrated to systematically decipher UV-B response mechanisms in E . sibiricus . Exposure to 288 kJ/m 2 UV-B radiation in tolerant (SC020 2-A1, SC) and sensitive (XJ007 22-A5, XJ) E . sibiricus genotypes yielded 21,773 genes, with 5,076 and 4,541 genotype-specific differentially expressed genes (DEGs), respectively. Temporal profiling of the DEGs revealed 3,792 and 6,322 DEGs in SC, compared to 4,826 and 10,890 DEGs in XJ under short- and long-term stress, respectively. Core findings demonstrated that MYB and WRKY transcription factors (TFs) mediated UV-B responses via phenylpropanoid metabolism and UVR8 signaling. In addition, 20 pivotal TFs, including EsMYB and EsbHLH, coordinated with 30 stress metabolites, such as corticosterone, to regulate the ascorbate and aldarate network, thereby activating 8 crucial pathways, including photosynthetic carbon fixation. Notably, heat shock proteins (HSP702 and HSP704) emerged as novel UV-B resistance components. These results provide molecular insights into UV-B adaptation of members of the Gramineae family and genetic resources for breeding UV-B radiation-resistant grass cultivars. • UV-B tolerance involves MYB/WRKY TFs and phenylpropanoid metabolism. • Key EsMYB/EsbHLH TFs coordinate with metabolites to activate core pathways. • Heat shock proteins HSP702/704 are novel components of UV-B resistance. • Study provides molecular insights for breeding UV-B resistant grasses.