The SlMED25-SlICE2 regulatory module controls cold stress adaptation in tomato.

The basic helix-loop-helix (bHLH) transcription factors ICEs (Inducer of CBF Expression) are pivotal regulators of plant cold stress responses, acting by orchestrating the transcription of COR (cold-responsive) genes. While the ICEs-dependent transcriptional control of COR genes expression remains poorly understood. As an evolutionarily conserved transcriptional coactivator, the Mediator complex bridges gene-specific transcription factors with the RNA polymerase II (Pol II) machinery to modulate gene transcription, yet whether and how Mediator complex participates in ICEs-dependent transcriptional regulation of COR genes remains unclear. In this study, using tomato (Solanum lycopersicum) as a model, we demonstrate that SlICE2 plays a critical role in cold stress tolerance via regulating COR genes expression. SlMED25, a Mediator subunit, physically interacts with SlICE2, and both proteins positively regulate cold stress responses. Importantly, SlMED25 acts as a transcriptional coactivator to promote SlICE2-mediated transcriptional activation during cold adaptation. Together, our results uncover a previously uncharacterized SlMED25-SlICE2 regulatory module that modulates cold stress responses through transcriptional coactivation, providing novel insights into the molecular mechanisms underlying plant cold tolerance.