Genome-Wide Identification of R2R3-MYB Family Members and Identification of AaMYB1/AaMYB36 Linked to Peel Coloration in Northern Red-Peel Actinidia arguta

Kiwiberry (Actinidia arguta) has been rapidly commercialized. However, fruits produced in northern growing regions predominantly have green peels, and the red/purple peel phenotypes remain relatively rare, which limits the discovery and utilization of red-peel germplasm. Peel reddening is primarily caused by the accumulation of anthocyanins, and R2R3-MYB transcription factors are key regulators of the flavonoid/anthocyanin biosynthetic pathway. However, the MYB transcription factor family in the genus Actinidia has been less studied, with few systematic analyses linked to color phenotypes. Therefore, we performed a genome-wide search for R2R3-MYB family members in A. arguta and characterized their physicochemical properties, phylogeny, chromosomal distribution, gene duplication events, and synteny relationships. Furthermore, RNA-Seq analysis, phylogenetic analysis, and gene expression patterns of the rare northern red-peel cultivar ‘Yanlong 1’ revealed that AaMYB1 and AaMYB36 are key candidate genes closely associated with anthocyanin biosynthesis in the fruit peel. Validation experiments revealed that both genes exhibited significantly higher expression during the coloration stage than during the green fruit stage, as well as significantly higher expression in the red-peel cultivar than in green-peel cultivars. Four key structural genes (UFGT, CHS, DFR, and ANS), especially, CHS, DFR, and ANS, displayed a similar pattern of upregulation. These correlative results suggest that AaMYB1 and AaMYB36 are candidate positive regulators of peel-specific anthocyanin accumulation. These results provide important targets for developing molecular markers and improving the red-peel trait in northern A. arguta through breeding.