RsNAC134 Regulates Taproot Skin Color via Positive Regulation of the Chlorophyll Degradation Pathway in Radish (Raphanus sativus)

The color of radish taproot skin is an important commercial quality trait that directly affects the visual judgment of consumers. The green/white coloration of radish taproots is caused by chlorophyll accumulation or fading; however, research on the mechanisms of color regulation in green/white variations remains limited. Therefore, we analyzed transcriptome data from the green radish ‘QZ-16’ and white radish ‘55’ and identified a key color-regulating gene, RsNAC134. The expression of RsNAC134 was significantly reduced in green radish ‘QZ-16’ but markedly increased in white radish ‘55’. Heterologous overexpression of RsNAC134 in transgenic tomatoes resulted in chlorotic phenotypes. Quantitative real-time polymerase chain reaction revealed significant upregulation of chlorophyll degradation pathway genes SlSGR and SlPAO in transgenic tomatoes. Similarly, in white radish, expression of the key chlorophyll degradation genes, RsSGR, RsPAO1, and RsPAO2, was notably increased. Yeast one-hybrid and luciferase assays demonstrated that RsNAC134 directly bound to the promoters of RsSGR, RsPAO1, and RsPAO2. These findings suggest that RsNAC134 regulates chlorophyll degradation by modulating RsSGR, RsPAO1, and RsPAO2 expression, ultimately influencing the radish color transition (loss of green pigmentation) or retention of green coloration. This work unravels novel regulatory factors of chlorophyll degradation and elucidates the molecular network governing chlorophyll degradation, providing crucial insights into the molecular basis of epidermal color variation in radish taproots.