Crosstalk between Brassinosteroid and Redox Signaling Contributes to the Activation of CBF Expression during Cold Responses in Tomato.

Brassinosteroids (BRs) play a critical role in plant responses to stress. However, the interplay of BRs and reactive oxygen species signaling in cold stress responses remains unclear. Here, we demonstrate that a partial loss of function in the BR biosynthesis gene resulted in lower whilst overexpression of led to increased levels of () transcripts. Exposure to cold stress increased BR synthesis and led to an accumulation of brassinazole-resistant 1 (BZR1), a central component of BR signaling. Mutation of BZR1 compromised the cold- and BR-dependent increases in and ) transcripts, as well as preventing hydrogen peroxide (HO) accumulation in the apoplast. Cold- and BR-induced BZR1 bound to the promoters of , and and promoted their expression. Significantly, suppression of expression compromised cold- and BR-induced accumulation of BZR1 and related increases in CBF transcripts. Moreover, -dependent HO production regulated BZR1 accumulation and the levels of CBF transcripts by influencing glutathione homeostasis. Taken together, these results demonstrate that crosstalk between BZR1 and reactive oxygen species mediates cold- and BR-activated CBF expression, leading to cold tolerance in tomato ().