MYB24 orchestrates terpene and flavonol metabolisms as light responses to anthocyanin depletion in grape variegated berries

The presence of naturally-occurring color mutants in plants has permitted the identification of many regulatory genes implicated in the synthesis of discrete metabolic compounds, mostly anthocyanins and carotenoids. Conversely, transcription factors that coordinate more than one specialized metabolic pathway seem challenging to screen from a forward genetics’ perspective. We explored the relationship between different branches of the phenylpropanoid and isoprenoid pathways while examining an infrequent berry skin color variegation in grapevine. Red and white berry skin sections were compared at the genetic, transcriptomic and metabolomic levels showing that light-responsive flavonols and monoterpenes increased in anthocyanin-depleted areas. We disclosed an enrichment of the corresponding pathways among up-regulated genes from white-skin sections, accompanied by increased expressions of flavonol regulators and the still uncharacterized MYB24 gene. We used DAP-seq to examine the in vitro binding of affinity‐purified MYB24 protein to genomic DNA and demonstrated its binding in the promoter regions of 22 terpene synthase genes, in addition to 32 photosynthesis/light-related genes, including the flavonol-regulator HYH. We confirmed the activation of TPS35 and HYH promoter-luciferase reporters in the presence of MYB24 and the grape bHLH-MYC2. The integration of several datasets allowed to define a list of high confidence targets, suggesting MYB24 as a modulator of light responses including the synthesis of flavonols and terpenes. The correspondence between MYB24 and monoterpenes in all conditions surveyed implies that this regulatory network is broadly triggered towards berry ripening, and that the absence of anthocyanin sunscreens accelerates its activation most likely in a dose-dependent manner due to increased radiation exposure. MYB24 DAP-Seq. Comparison between MYB24 library (one replicate) against pHALO library (one replicate) as negative control.