Genome‑Wide Identification of NAC Transcription Factors in Elymus sibiricus and Functional Characterisation of EsNAC29 in Light Inhibition

Elymus sibiricus L., a perennial grass critical for livestock production and ecological restoration on the Qinghai-Tibet Plateau, is frequently exposed to intense high-altitude light stress. NAC transcription factors are key regulators of plant development and stress responses, yet they remain uncharacterised in E. sibiricus. Here, we reported the first genome-wide analysis of the NAC family in this allotetraploid species and identified 290 EsNAC genes. These genes are classified into 14 subfamilies, 11 of which have undergone significant expansion mainly through segmental duplication events, a process that may contribute to adaptation on the Qinghai-Tibet Plateau. We observed pronounced enrichment of light-responsive cis-elements in the promoters of EsNAC genes. Consistent with this, we identified a significant overlap between Arabidopsis AtNAC genes and a set of light-repressed genes, implicating the NAC family in light-inhibition pathways. To explore how E. sibiricus copes with high-light stress, we functionally characterised EsNAC29, a homologue of Arabidopsis ANAC029/AtNAP. Heterologous overexpression of EsNAC29 in Arabidopsis recapitulated a strong light-inhibition phenotype, including chlorosis and dwarfism, with the chlorophyll content, plant height, and fresh weight reduced by more than 32%, 48%, and 80%, respectively. Transcriptomic profiling revealed that EsNAC29 represses chlorophyll-biosynthesis and photosynthesis-related genes while up-regulating light-repressed and defence-related pathways. These findings establish EsNAC29 as a key negative regulator of photosynthesis and an integrative node that links light perception with stress adaptation, providing molecular insights into how the grasses of the plateau acclimate to intense light environments.