A SIP1 gene of Trihelix family, SlGT-33, promotes chilling tolerance and fruits set under prolonged cold stress in tomatoes.

backgroundTrihelix 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.

resultsSlGT-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.

conclusionsCollectively, 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.