CmTCP9/12/25-CmSAUR1 module assists trehalose-induced cold tolerance in melon seedlings

Cold stress negatively affects melon growth and development. Previous studies have shown that exogenous trehalose (Tre) alleviates the cold damage in melon seedlings; however, the specific mechanism is not fully clarified. Here, Tre treatment increased the indole-3-acetic (IAA) content and upregulated an early response factor of IAA (small auxin up RNA gene, CmSAUR1 ) gene expression. Inhibition of IAA signal transport or silencing of CmSAUR1 decreased the activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase. This led to increased susceptibility to cold damage in melon seedlings and diminished the beneficial impact of Tre. Through the analysis of transcriptome and promoter of CmSAUR1 , the upstream transcription factor CmTCP9/12/25 of CmSAUR1 was excavated. Protein–DNA interaction experiments further verified that CmTCP9/12/25 could transcriptionally regulate CmSAUR1 expression. Yeast two-hybrid, luciferase complementation imaging and bimolecular fluorescence complementation experiments further confirmed that CmTCP9/12 interacted with CmTCP25 to form protein complexes. Silencing CmTCP9/12/25 genes significantly aggravated the cold damage of melon seedlings and weakened the efficacy of Tre. All of them downregulated the expression of CmSAUR1 . In conclusion, application of Tre induced the upregulation of CmTCP9/12/25 , and CmTCP9/12/25 could bind to the CmSAUR1 promoter and activate its expression. These eventually increased the cold tolerance of melon seedlings.