The impact of awn length on seed yield and drought resistance in Elymus sibiricus L. and the molecular mechanism underlying awn length regulation.

BACKGROUND: Elymus sibiricus L. is a native grass species vital for ecological restoration and livestock production on China's Qinghai-Tibet Plateau, valued for its high yield, superior quality, and strong adaptability. Its awns, a significant morphological structure of the seed, significantly influence seed yield and stress resistance. This study utilized 14 E. sibiricus accessions with distinct awn lengths to investigate the influence of awn length on seed yield and drought resistance. Additionally, it aims to elucidate the molecular mechanisms underlying awn length regulation in E. sibiricus. RESULTS: Analysis of five agronomic traits related to seed yield revealed a significant positive correlation between awn length and thousand-grain weight. Principal component analysis and cluster analysis classified the 14 accessions into the long-awned and short-awned groups, with the long-awned group exhibiting higher seed yield potential. Anatomical analysis of awn tissues of the QH002 and GS002 accessions during four stages-heading, flowering, filling, and milk ripening-revealed that the long-awn genotype possessed more developed structures including parenchyma cells, sclerenchyma cells, vascular bundles, and stomata. These structures endows it with enhanced conduction, support, and defense functions. Transcriptome analysis of middle spikes from the QH002 and GS002 genotypes revealed 6,321 differentially expressed genes (DEGs), primarily enriched in metabolic pathways such as photosynthesis, galactose metabolism, and tyrosine metabolism. Among them, two photosystem II-related genes (EsiS02g0031800, EsiH02g0028770) and 11 DEGs associated with carbohydrate metabolism were identified as key candidate genes. Under terminal drought stress, the long-awned accession (QH002) exhibited higher relative water and proline content, and increased antioxidant enzyme activities, compared to the short-awned accession (GS002), whereas malondialdehyde content was higher in the latter. These results indicate that the long-awned accessions possesses enhanced drought tolerance compared to the short-awned accessions. CONCLUSIONS: This study demonstrated that long-awned E. sibiricus exhibits higher seed production potential and stronger drought resistance, providing new insights and theoretical support for the breeding of high-yielding and stress-tolerant E. sibiricus varieties. It further adds to our understanding of the molecular mechanisms governing awn morphogenesis and length determination.