The tomato WRKY32 transcription factor affects ripe fruit color by regulating YFT1, a core component of ethylene signal transduction.

Fruit quality in most fleshy fruit crops is fundamentally linked to ripening associated traits, including changes in color. In many climacteric fruits, including tomato (Solanum lycopersicum), the phytohormone ethylene plays a key role in regulating ripening. Previous map-based cloning of YFT1 revealed that it encodes the EIN2 protein, a core component in ethylene signal transduction. A YFT1 allele with a genetic lesion was found to be downregulated in the yft1 tomato mutant that has a yellow-fruited phenotype and perturbed ethylene signaling. Here we report that the WRKY32 transcription factor regulates tomato fruit color formation, based on bioinformatic analysis, yeast one hybrid assays and electrophoretic mobility shift assays. WRKY32 binds to W-box and W-box-like motifs in the regulatory region of the YFT1 promoter and induces its expression. In WRKY32-knockdown tomato fruit, ethylene signaling is reduced, leading to a suppression in ethylene emission, a delay in chromoplast development, decreased carotenoid accumulation and a yellow-fruited phenotype. These results provide new insights into the regulatory networks that govern tomato fruit color formation via ethylene signal transduction.