Physiological and transcriptomic insights into the roles of growth and defense hormones in bermudagrass shade tolerance.

Bermudagrass (Cynodon dactylon) is widely used in ecological restoration, soil conservation, industrial landscaping, and potentially bioenergy, ethanol, and biochar production. Shading critically influences bermudagrass growth and survival. However, current knowledge on bermudagrass responses to shade from a hormonal perspective, particularly regarding growth and defense mechanisms, remains limited. We investigated shade responses in bermudagrass with two accessions, shade-tolerant (C792) and shade-sensitive (GZ), through morphological, physiological (hormone profiling by UPLC-MS), and transcriptomic (|log2FC| > 1, adjusted P < 0.05) analyses. Under shading, C792 decreased less on shoot density, coverage, and clipping dry weight than GZ, while maintaining leaf thickness and increasing turf height. Shading significantly increased indole-3-acetic acid (IAA) and gibberellin 1 (GA1) concentrations in C792 but not GZ, with corresponding upregulation of GA biosynthesis genes, changes correlated with its shade tolerance; furthermore, the expression of GA signaling-related gene GID1 was down-regulated to a lesser extent in C792 than GZ, while the up-regulation extent of DELLA was also less in C792 than GZ. Although cis-12-Oxo-Phytodienoic Acid (cis-OPDA) increased under shading, JA concentration remained stable in both bermudagrass under shading. C792 exhibited upregulated jasmonate ZIM domain 1 (JAZ1) and JAZ2 but downregulated salicylic acid (SA) concentrations, whereas GZ exhibited opposite trends. Notably, the SA pathway gene NPR1 in C792 downregulated significantly more pronounced than that in GZ. These coordinated hormonal adjustments in C792, associated with increased growth-promoting hormones (IAA/GA1) contents while showed adjustments in defense responses (reduced JA response), consistent with its shade adaptation through minimal growth trade-offs and strategic defense modulation.