The CsWRKY3-CsHB7 transcriptional cascade promotes temperature-responsive peel pigmentation via CsCCD4b-mediated...

Plant coloration, a key trait for attracting pollinators and seed dispersers, is dynamically adjustable in response to temperature. However, the molecular mechanisms underlying temperature-dependent peel pigmentation in citrus remain poorly understood. In this study, through a multi-site geographical analysis of Newhall navel oranges across 32 locations in China, we revealed a distinct latitudinal distribution of oranges, with redder peel coloration at higher latitudes. Subsequent correlation analysis and postharvest treatments pinpointed the suboptimal low temperature range of 10°C-16°C as the primary determinant for the peel pigmentation. Combined transcriptomic and functional analyses identified CsHB7 as an essential early regulator mediating low-temperature-induced peel pigmentation. Further investigation unveiled a CsWRKY3-CsHB7 transcriptional cascade that directly responds to low temperature and promotes peel pigmentation by activating the expression of CsCCD4b, which encodes a key enzyme for the synthesis of the red pigment β-citraurin. Moreover, we demonstrated that the CsWRKY3-CsHB7 module, mediated by the W-box cis-element in the CsHB7 promoter, contributes to natural variation in suboptimal low-temperature-induced pigmentation. Our findings decrypt a key regulatory mechanism of citrus peel pigmentation, reveal a genetic basis for further evolutionary studies, and provide molecular tools for climate-resilient citrus breeding.