Physiological and Transcriptomic Profiling of Exogenous Jasmonic Acid-Mediated Cold Tolerance in Seedlings of Poa pratensis var. anceps cv. Qinghai

Poa pratensis var. anceps cv. Qinghai is a high-quality forage grass widely distributed across the Qinghai–Tibetan Plateau, exhibiting exceptional cold tolerance, a well-developed root system, and outstanding soil consolidation capacity, rendering it of great significance for ecological management in alpine regions. Jasmonic acid (JA), as an endogenous phytohormone, plays a pivotal role in regulating low-temperature adaptation and is hypothesized to be a core regulatory hormone underlying the cold tolerance of this cultivar. In this study, using seedlings of P. pratensis var. anceps cv. Qinghai (PQ) and the cold-sensitive cultivar P. pratensis “Barun” (PB) as a control, exogenous methyl jasmonate (MeJA, a JA analog) and the JA biosynthesis inhibitor DIECA were applied, and physiological and transcriptomic analyses were conducted to elucidate the mechanism by which JA regulates low-temperature adaptation. The results showed that MeJA significantly alleviated the growth inhibition induced by low temperature (4 °C) in both materials, with a more pronounced effect in PQ. Specifically, compared with the corresponding cold-only controls, MeJA treatment increased chlorophyll content by 5.55% in PQ and 22.40% in PB after 72 h of cold stress; soluble sugar content by 61.40% and 33.40%; soluble protein content by 47.16% and 36.50%; and proline content by 80.82% and 59.17%, respectively. MeJA also enhanced antioxidant enzyme activities, with SOD increasing by 49.28% and 15.61%, POD by 73.93% and 43.10%, CAT by 36.68% and 12.95%, and APX by 53.05% and 21.10% in PQ and PB, respectively. Additionally, non-enzymatic antioxidant contents (GSH and AsA) increased by 15.55% and 48.31% in PQ, versus 3.37% and 19.54% in PB. In contrast, DIECA suppressed these enhancements, with a more distinct inhibitory effect on PB, confirming that the JA pathway is a critical mechanism mediating low-temperature response in PQ, with significantly higher regulatory efficiency than that in the control. Transcriptome sequencing generated 1.787 million transcripts and identified 16,267 differentially expressed genes (10,054 up-regulated, 6213 down-regulated) in the MeJA-treated PQ group. GO and KEGG enrichment analyses revealed pathways associated with photomorphogenesis and carotenoid biosynthesis. Weighted gene co-expression network analysis (WGCNA) identified two core modules, and eight key genes including PpHY5 and PpCOR410 were screened, suggesting their coordinated roles in JA-mediated cold tolerance. These findings provide a comprehensive physiological and transcriptomic basis for understanding JA-enhanced cold tolerance in PQ seedlings.