Figure 7.

Model for the positive feedback regulatory loop between ABA metabolism and carotenoid metabolism mediated by the transcriptional regulatory module CsERF110–CsERF53 in citrus.

CsERF110 responds to ABA signaling and activates the expression of multiple carotenogenic genes (CsGGPPS, CsPSY, CsPDS, CsCRTISO, CsLCYB2, CsLCYE, CsHYD, and CsNCED2) to promote carotenoid accumulation. Meanwhile, CsERF53 is not only induced by ABA signaling but also directly activated by ERF110, which in turn activates the expression of several carotenogenic genes (CsGGPPS, CsPSY, CsHYD, and CsNCED2), ultimately promoting carotenoid biosynthesis. In addition, CsERF110 interacts with CsERF53, and their interaction further enhances their activation of downstream carotenogenic genes. In turn, ABA, as a ripening signal, significantly induces the regulation and interaction of CsERF110 and CsERF53 in feedback regulation, thereby promoting carotenoid biosynthesis and fruit coloration. In general, a positive feedback regulatory loop between the CsERF110–CsERF53 regulatory module and ABA signaling determines carotenoid biosynthesis in citrus.