Anthocyanin accumulation in Actinidia arguta during the postharvest period is controlled by MYB-associated activation and repression

The development of new selections of fruit species is often driven by novel appearance and pleasant eating experiences. Kiwiberry ( Actinidia arguta ) is one such fruit; a kiwifruit relative that is both novel in appearance and easily consumed because of an edible skin. Most varieties of this fruit are green or red. Here we show that anthocyanins accumulation in the flesh of kiwiberry during the postharvest is driven by the R2R3 MYB transcription factor, AaMYB110 . However, expression of AaMYB110 also occurs in green stages, suggesting other controlling elements. A screen of repressive transcription factors showed that the R2R3 MYB AaMYB4 strongly inhibited AaMYB110 activity. Expressing the MYB activator in green tissue resulted in accumulation of red anthocyanins, but this was significantly inhibited by the presence of R2R3 MYB4. In studying this transcriptional repressor were discovered direct and indirect roles that the EAR motif in the c-terminus of AaMYB4 has in inhibiting anthocyanin synthesis, and the inhibitory effect of EAR is conserved in other plants. In summary, our data reveal the critical role of the AaMYB110-AaMYB4 associated activation and repression module in regulating anthocyanin accumulation in kiwiberry during the postharvest period