The transcription factor CaBBX20 regulates capsanthin accumulation in pepper (Capsicum annuum L.)

Carotenoids are important pigments whose accumulation is regulated by transcription factors such as those from the MADS-box and MYB families. BBXs are a kind of zinc finger transcription factors with one or two B-box domains, which were identified involved in photomorphogenesis. However, little is known about the function of CaBBX in the pigmentation of pepper fruit (Capsicum annuum). Here, we selected two red-fruited pepper cultivars to investigate carotenoid contents at three developmental stages (Mg: mature green stage, Tf: turning stage, and Rf: ripen stage) during fruit ripening (30, 45 and 60 days after flowering). Our results showed that carotenoid accumulation in pepper fruits begins at turning stage (Tf) and peaks in ripen stage (Rf), which was reflected in the fruit color change (from green to brown, and then to red). The expression of CaBBX20 was upregulated with the pigmentation during fruit ripening. Silencing CaBBX20 led to reduced carotenoid accumulation, as well as downregulated expression of CaCCS, suggesting a positive role of CaBBX20 in carotenoid metabolism of pepper fruit. Our study thus provides basic insight into carotenoid biosynthesis during pepper fruit pigmentation.