Abstract
BACKGROUND: Trihelix factors play important roles in improving plant resistance to abiotic stress, however, the role of SIP1 subfamily contributing to cold tolerance was rarely reported in tomatoes. Here, we isolated a cold-repressed gene, SlGT-33, from the tomato and found it vital biological function in morphological development and adaptation to prolonged chilling stress. RESULTS: SlGT-33 belonged to SIP1 clade and was localized to cell nucleus. SlGT-33 was specifically expressed in mature leaves and stems, induced by ABA and dehydration, and repressed by GA and low temperature. Overexpression of SlGT-33 suppressed the chlorophyll synthesis but promoted fruits set than control under prolonged cold conditions. Transcriptome and metabolome analysis demonstrated that SlGT-33 OE lines have higher vitality and antioxidant capacity than control. Concomitantly, SlCBFs, SlICE1, and SlAPX2 were significantly upregulated in SlGT-33 OE lines along with high activity of SOD, POD and CAT. Interestingly, most of the top upregulated DEGs were located at specific loci on chromosome 2, a potential site of photosynthesis. Bioinformatic analysis revealed that the GA elements are present in their promoters. EMSA assay confirmed that SlGT-33 binds to GA elements and directly regulates the expression of ICE1 and CaM6. Y2H assays demonstrated that SlGT-33 interacts with ICE1 but not with CaM6. To investigate the reason for early fruits set, we detected higher GA contents and lower ABA levels by HPLC in SlGT-33 OE lines. Moreover, genes involved in GA synthetic and response were significantly upregulated in SlGT-33 OE lines. CONCLUSIONS: Collectively, this study demonstrated that SlGT-33 enhances cold tolerance and early fruits set under prolonged chilling stress by upregulating antioxidant capacity, interacting with ICE1, directly inducing the expression of ICE1 and CaM6, and promoting GA synthesis.