Isolation of anthocyanin biosynthetic genes in red Chinese sand pear (Pyrus pyrifolia Nakai) and their expression as affected by organ/tissue, cultivar, bagging and fruit side

Recently, red Chinese sand pears (Pyrus pyrifolia Nakai) have become widely cultivated throughout China. To clarify the molecular mechanism underlying anthocyanin accumulation in red Chinese sand pears, genes encoding the anthocyanin biosynthesis enzymes including phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS) and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) were isolated from the mature fruit of ‘Meirensu’ pears and were designated as PpPAL, PpCHI, PpCHS, PpDFR, PpF3H, PpANS and PpUFGT, respectively. The expression of PyMYB10 and all seven anthocyanin biosynthetic genes were detected in two red pear cultivars under fruit bagging treatments during fruit maturation. The transcription level of all these genes was markedly up-regulated in two cultivars and peaked at 1 DABR (days after the bag removal) followed by a decline. All seven anthocyanin biosynthetic genes were differentially expressed among various organs or tissues, and none was fruit specific. Higher mRNA abundance of all seven anthocyanin biosynthetic genes and PyMYB10 was detected in the skin of sun-side ‘Yunhongli No. 1’ than in ‘Meirensu’ in all surveys, and in the skin of sunlit side of ‘Meirensu’ (M) than in the skin of the shaded side of ‘Meirensu’ which positively correlated with anthocyanin accumulation. Our results suggest that (1) anthocyanin accumulation in fruit of red Chinese sand pears was closely related to the coordinated expression of PyMYB10 and multiple biosynthetic genes and the level was modified by the genetic background of cultivars, and (2) light exposure after bag removal enhanced anthocyanin accumulation by inducing the expression of PyMYB10 and the anthocyanin biosynthetic genes. The results obtained in this study will be helpful in understanding the molecular mechanism of anthocyanin accumulation in red Chinese sand pears and can serve as the basis for the development of marker-assisted selection or for anthocyanin metabolic engineering of pears.