Functional Characterization of VvSK Gene Family in Grapevine Revealing Their Role in Berry Ripening

The glycogen synthase kinase 3/shaggy kinase (GSK3) is a serine/threonine kinase that plays important roles in brassinosteroid signaling, abiotic stress responses, cell division, and elongation, etc. In this study, we characterized seven grape GSK3 genes, showing high similarities with homologs from other species includingArabidopsis, white pear, apple, orange, and peach. Gene chip microarray data derived from an online database revealed very diverse developmental and tissue-specific expression patterns ofVvSKs.VvSK3andVvSK7showed much higher expression levels in almost every tissue compared with other members.VvSK7was highly enriched in young tissues like berries before the veraison stage, young leaves and green stems, etc., but immediately downregulated after these tissues entered maturation or senescence phases. Prediction of cis-elements inVvSKpromoters indicated thatVvSKsmight be sensitive to light stimulation, which is further confirmed by the qPCR data. Constitutive overexpression ofVvSK7inArabidopsisleads to dwarf plants that resembles BR-deficient mutants. The photosynthetic rate was significantly reduced in these plants, even though they accumulated more chlorophyll in leaves. Transient overexpression ofVvSKsin tomatoes delayed the fruit ripening process, consistent with the observation in grapevine which blocksVvSKsby EBR- or BIKININ-promoted berry expansion and soluble solids accumulation. Data presented in the current study may serve as a theoretical basis for the future application of BRs or related compounds in quality grape production.Keywords:GSK3;grapes;evolutionary analysis;light response;photosynthesis;ripening