TheHY5andMYB15transcription factors positively regulate cold tolerance in tomato via theCBFpathway

The induction of C-repeat binding factors (CBFs) is crucial for plant survival at low temperatures. Therefore, understanding the mechanisms that regulateCBFtranscription is vital for the future development of crops with increased cold tolerance. Here, we provide evidence for the existence of a LONG HYPOCOTYL 5 (HY5)-MYB15-CBFs transcriptional cascade that plays a crucial role in the cold response in tomato. The exposure of tomato plants to cold (4 degrees C) increased the levels ofHY5,MYB15andCBFstranscripts. Moreover, mutations inHY5orMYB15decreased the levels ofCBFtranscripts. In contrast, overexpression ofHY5orMYB15increasedCBFtranscript abundance. Crucially, the HY5 transcription factor activated the expression ofMYB15by directly binding to the promoter region, while both HY5 and MYB15 activated the expression ofCBF1,CBF2andCBF3.Taken together, these data show that HY5 can directly regulateCBFtranscript levels, and also influenceCBFexpression indirectly via MYB15. The coordinated action of HY5 and MYB15 allows precise regulation ofCBFexpression and subsequent cold tolerance. These findings provide an improved understanding of the molecular mechanisms affording transcriptional regulation of CBFs, which can be exploited in the future to enhance cold tolerance in crops.