Differential morpho-physiological traits and hormone signal transduction pathway of Kentucky bluegrass cultivars in response to drought stress

Kentucky bluegrass (Poa pratensis L.) is a widely used cool-season turfgrass in the world. However, the underlying responses of drought-induced morpho-physiology and gene regulation remain to be elucidated for this grass species. This study examines the phenotypic, physiological, and transcriptional differences between the drought-tolerant cultivar ‘Maoershan’ and the drought-sensitive cultivar ‘Brilliant’ under varying levels of drought stress, aiming to identify phenotypic traits and key pathways associated with different drought-resistant varieties. Under different levels of drought stress, ‘Maoershan’ exhibited stronger drought adaptability, characterized by a slower decline in turf quality, morphological indicators and photosynthetic efficiency, alongside a greater increase in soluble sugar content and antioxidant enzyme activities. In contrast, ‘Brilliant’ showed more pronounced membrane damage and hormone imbalance. Transcriptome analysis identified 75,166 differentially expressed genes (DEGs). Under the same drought condition, the number of DEGs in ‘Brilliant’ was higher, and the changes in gene expression observed in the ‘Brilliant’ were more significant than those in the ‘Maoershan’. Weighted gene co-expression network analysis (WGCNA) revealed a key gene module highly correlated with drought tolerance. This module was significantly enriched in the plant hormone signal transduction pathway, particularly the abscisic acid (ABA) signaling pathway. Further analysis revealed that changes in ABA signaling pathway gene expression in ‘Maoershan’ were more stable than those in ‘Brilliant’ as drought progressed, such as PP2C37 (Cluster-4199.118277), ABI5 (Cluster-4199.122824), and SAPK4 (Cluster-4199.57749). These findings indicated that the differences in gene expression of the ABA signal transduction pathway conferred better drought tolerance in ‘Maoershan’ than in ‘Brilliant’. This study could help elucidate the mechanisms underlying drought tolerance in Kentucky bluegrass, thereby facilitating genetic improvements aimed at reducing water input in turfgrass management.