FaMADS6 negatively regulates anthocyanin accumulation in strawberry by inhibiting FaMYB10 expression and ABA biosynthesis

Abstract

Anthocyanins are the main pigments in ripe strawberry fruits. FaMYB10 and abscisic acid (ABA) are the two major regulators of anthocyanin biosynthesis in the maturation process of strawberry fruits. However, the transcriptional regulation of FaMYB10, ABA biosynthesis, and anthocyanin accumulation in strawberry (Fragaria × ananassa) remain largely unknown. Here, a yeast one-hybrid screen using the FaMYB10 promoter identified a class B MADS-domain transcription factor, FaMADS6 in strawberry. FaMADS6 exhibited high expression at the early developmental stage but was hardly detected during maturation of strawberry fruit, a pattern opposite to accumulation of anthocyanins. Transcriptional upregulation of FaMADS6 repressed anthocyanin accumulation and expression of FaMYB10 and the anthocyanin biosynthetic genes, FaCHS, FaCHI, FaF3H, FaANS, and FaUFGT. In contrast, downregulation of FaMADS6 promoted the expression of FaMYB10 and the anthocyanin biosynthetic genes. The promoters of the anthocyanin biosynthetic genes were not directly bound by FaMADS6, in contrast to FaMYB10. Analysis of the DNA binding sequences of FaMADS6 revealed that it also interacted with the promoters of FaNCED2 and FaPYR1, which are involved in the biosynthesis and perception of ABA. Overexpression of FaMADS6 significantly suppressed FaNCED2 and FaPYR1 and ABA synthesis in transgenic strawberry. Together, our findings suggest that FaMADS6 functions as a suppressor of anthocyanin accumulation by directly downregulating FaMYB10 and ABA production during strawberry fruit maturation.