Unraveling branch point–driven SR45a splicing dynamics in heat stress for plant adaptation

Heat stress impairs plant development by disrupting essential molecular processes. Alternative splicing (AS) is emerging as a key regulatory mechanism in heat responses, yet how stress-responsive AS is fine-tuned within core splicing regulators remains underexplored. Here, we uncover a heat-activated, autoregulatory splicing switch in the serine/arginine-rich factor SR45a, critically dependent on intron 4. Using an intron 4–based luciferase reporter, we show that heat enhances intron removal, promoting the full-length isoform over truncated variants. This switch relies on branch point (BP) recognition, with SR45a and cap-binding protein 20 (CBP20) coordinating BP-dependent splicing under stress. Overexpression of either protein enhances thermotolerance by stabilizing AS dynamics. HSFA2 directly activates SR45a transcription, linking transcriptional and splicing control. Notably, intron 4–mediated splicing is conserved in both maize and wheat, suggesting its potential as a portable regulatory module in crops. Our study establishes a stress-inducible SR45a-CBP20-BP axis and introduces an intron-based strategy for engineering thermotolerance via precision splicing control.