Identification of Flavonoid 3′-Hydroxylase Genes from Red Chinese Sand Pear (Pyrus pyrifolia Nakai) and Their Regulation of Anthocyanin Accumulation in Fruit Peel

The red Chinese sand pear (Pyrus pyrifolia Nakai) is native to China and exhibits a unique fruit coloration pattern. Flavonoid 3′-hydroxylase (F3′H) catalyzes the hydroxylation of flavonoids, which subsequently determines the components of anthocyanins and the color of plant organs. Two genes encoding flavonoid 3′-hydroxylase (F3′H), PpF3′HI and PpF3′HII, have been identified in red Chinese sand pears. The coding regions for PpF3′HI and PpF3′HII were 1542 and 1536 bp in length, respectively. PpF3′HI shared 95% of its amino acid sequence identity with PpF3′HII, and a highly conserved P450 superfamily domain was found both in PpF3′HI and in PpF3′HII. Phylogenetic analysis showed that PpF3′HI and PpF3′HII clustered with MdF3′HI and MdF3′HII, respectively. PpF3′H genes were highly expressed in anthocyanin-enriched tissues such as young leaves, and transcription of PpF3′H genes corresponded to anthocyanin biosynthesis during the developmental stages, bagging treatment, and postharvest UV-B/visible irradiation treatment. A Y1H assay showed that PpMYB10 and PpHY5 could interact with the −419 bp to 0 bp and −746 bp to −396 bp fragments of the PpF3′HI promoter region, respectively. Understanding the mechanism of flavonoid hydroxylation patterns will, in turn, promote the development of new technologies for modifying flavonoid and anthocyanin composition in fruits.