Integrative physiological and transcriptomic analysis identifies candidate genes and co-expression networks associated with cold tolerance in Kentucky Bluegrass (Poa pratensis L.)

Low-temperature stress restricts plant growth, development, and geographical distribution. Kentucky bluegrass ( Poa pratensis L.), a cool-season turfgrass, is susceptible to low-temperature events during winter, early spring, and late autumn, which can impair turf establishment and quality. To investigate the physiological and molecular responses associated with cold tolerance in Kentucky bluegrass, 20 accessions were evaluated at the germination stage under 7 °C and at the seedling stage under 0 °C, with 25 °C serving as the control. Based on comprehensive cold-tolerance evaluation, MD and XH were selected as representative cold-tolerant and cold-sensitive accessions, respectively. Compared with XH, MD maintained higher superoxide dismutase, peroxidase, and catalase activities, accumulated more soluble protein and proline, exhibited lower levels of H₂O₂, O₂·⁻, malondialdehyde, and relative electrical conductivity, and maintained more stable photosynthetic performance under low-temperature stress. Transcriptome profiling of MD and XH at 0, 24, and 48 h under 0 °C revealed distinct genotype-dependent transcriptional responses. Differentially expressed genes and genes within trait-associated co-expression modules were primarily enriched in plant hormone signal transduction, mitogen-activated protein kinase signaling, phenylpropanoid biosynthesis, starch and sucrose metabolism, and plant-pathogen interaction pathways. These results identify MD as a promising cold-tolerant germplasm and provide candidate genes and co-expression networks associated with cold tolerance, offering physiological and molecular resources for future genetic improvement of Kentucky bluegrass.