Jasmonic Acid Biosynthesis and the Activation of Signal Transduction Pathway Play a Crucial Role in Alfalfa Adaptation to Drought Stress

Drought severely impacts alfalfa yield. This study compared drought-tolerant “Zhaodong” (ZD) and sensitive “Zhongmu No.1” (ZM) cultivars. ZD maintained superior photosynthetic activity and osmotic adjustment under drought. Integrated transcriptomic and WGCNA analyses identified the JA synthesis gene MsOPR1 as a key regulator. MsOPR1 overexpression enhanced drought tolerance by protecting photosynthesis, reducing ROS, and improving osmotic adjustment. MsOPR1 promoted JA accumulation, which down-regulated MsJAZ3A and activated the transcription factor MsMYC2 . MsMYC2 itself was induced by drought and JA, and its overexpression positively regulated drought resistance and JA signaling. In conclusion, JA synthesis and signaling activation, mediated by MsOPR1 and MsMYC2, are crucial for alfalfa drought adaptation, providing candidate genes and a theoretical basis for molecular breeding.