Deciphering the regulatory network of the NAC transcription factor FvRIF, a key regulator of strawberry (Fragaria vesca) fruit ripening.

The NAC transcription factor RIF (Ripening Inducing Factor) was previously reported to be necessary for the ripening of octoploid strawberry (Fragaria × ananassa) fruit, but the mechanistic basis of RIF-mediated transcriptional regulation and how RIF activity is modulated remains elusive. Here we show that FvRIF in diploid strawberry, Fragaria vesca, is a key regulator in the control of fruit ripening, and that knockout mutations of FvRIF result in a complete block of fruit ripening. DNA affinity purification sequencing coupled with transcriptome deep sequencing suggests that 2080 genes are direct targets of FvRIF-mediated regulation, including those related to various aspects of fruit ripening. We provide evidence that FvRIF modulates anthocyanin biosynthesis and fruit softening by directly regulating the related core genes. Moreover, we demonstrate that FvRIF interacts with and serves as a substrate of mitogen-activated protein kinase 6 (FvMAPK6), which regulates the transcriptional activation function of FvRIF by phosphorylating FvRIF at Thr-310. Our findings uncover the FvRIF-mediated transcriptional regulatory network in controlling strawberry fruit ripening and highlight the physiological significance of phosphorylation modification on FvRIF activity in ripening.