ABA/JA activated bHLH transcription factor PalBH1 is involved in cold tolerance in Pennisetum alopecuroides

Cold stress severely restricts plant growth by inducing oxidative damage and photosynthetic inhibition. Although basic helix-loop-helix (bHLH) transcription factors are implicated in stress responses, their role in Pennisetum cold adaptation remains unclear. Here, we identified a cold-tolerant accession P. alopecuroides cv. ‘Liqiu’(LQ). Transcriptome and weighted gene co-expression network analysis (WGCNA) pinpointed PaIBH1 ( P. alopecuroides ILI1 BINDING bHLH ), a bHLH transcription factor, as a central hub gene induced by cold. Heterologous overexpression of PaIBH1 enhanced cold tolerance in Arabidopsis by stabilizing photosynthesis, maintaining membrane integrity, and boosting antioxidant capacity, without compromising plant growth—a trait combination of considerable agronomic relevance. Its promoter harbors abscisic acid (ABA)- and jasmonate (JA)-responsive elements, and both hormones accumulated under cold stress. Inhibiting ABA or JA synthesis suppressed PaIBH1 expression and increased cold sensitivity. Luciferase reporter assays further showed that PaIBH1 transcriptionally activates PaNAC019 and PaHAI2. PaIBH1 coordinates cold resistance by regulating stress-responsive processes and upregulating downstream genes involved in stress response and ROS scavenging. Our study reveals that PaIBH1 , activated by ABA and JA signaling, enhances cold adaptation in P. alopecuroides and provides a genetic resource for improving cold tolerance in forage grasses.