WUSCHEL-Related Homeobox Transcription Factor SlWOX13 Regulates Tomato Fruit Ripening.

Fruit ripening is a complex, genetically programmed process involving the action of critical transcription factors (TFs). Despite the established importance of WUSCHEL-related homeobox (WOX) TFs in plant development, the involvement of WOX and its underlying mechanism in the regulation of fruit ripening remain unclear. Here, we demonstrate that SlWOX13 regulates fruit ripening in tomato (Solanum lycopersicum). Overexpression of SlWOX13 accelerates fruit ripening, whereas loss-of-function mutation in SlWOX13 delays this process. Moreover, ethylene synthesis and carotenoid accumulation are significantly inhibited in slwox13 mutant fruit, but accelerated in SlWOX13 transgenic fruit. Integrated analyses of RNA-seq and ChIP-seq identified 422 direct targets of SlWOX13, of which 243 genes are negatively regulated and 179 are positively regulated by SlWOX13. EMSA, RT-qPCR, DLR and ChIP-qPCR analyses demonstrated that SlWOX13 directly activates the expression of several genes involved in ethylene synthesis and signaling and carotenoid biosynthesis. Furthermore, SlWOX13 modulates tomato fruit ripening through key ripening-related TFs, such as RIN (RIPENING INHIBITOR), NOR (NON-RIPENING) and NAC4 (NAM, ATAF1, 2, and CUC2 4). Consequently, these effects promote fruit ripening. Taken together, these results demonstrate that SlWOX13 positively regulates tomato fruit ripening via both ethylene synthesis and signaling and by transcriptional regulation of key ripening-related transcription factors.