Enhancing cold tolerance through HubZIP6-mediated CBF activation and salicylic acid signaling in pitaya

Abstract

Cold stress severely limits the yield and quality of fruit crops, yet its regulatory mechanisms in pitaya remain poorly understood. Here, we identified a cold-inducible bZIP transcription factor, HubZIP6, that plays a central role in enhancing cold tolerance in pitaya. HubZIP6 is a nuclear-localized protein with transcriptional activation activity, and its overexpression in Arabidopsis and tomato significantly improved cold tolerance, as reflected by higher survival rates, reduced ion leakage, and lower reactive oxygen species accumulation. Mechanistically, HubZIP6 directly binds to ACGT motifs in the promoters of HuCBF1 and HuCBF3, thereby activating their expression under cold stress. In addition, HubZIP6 physically interacts with the salicylic acid-binding protein HuSABP2, which synergistically enhances the transcriptional activation of HuCBF genes. Notably, HubZIP6 also directly activates HuSABP2, forming a regulatory loop that connects CBF transcriptional control with salicylic acid signaling. Consistently, overexpression of HuSABP2 further enhances cold tolerance in transgenic plants. Collectively, these findings demonstrate that cold tolerance is enhanced through HubZIP6-mediated integration of CBF activation and salicylic acid signaling, providing a promising genetic target for improving stress resilience in fruit crops.