Comparison of phenolic metabolism and primary metabolism between green ‘Anjou’ pear and its bud mutation, red ‘Anjou’

Abstract

Green 'Anjou' pear and its bud mutation, red 'Anjou' were compared to understand their differences in phenolic metabolism and its effect on primary metabolism. In the flesh of the two cultivars, no difference was detected in the concentration of any phenolic compound, the transcript level of MYB10 or the transcript levels or activities of key enzymes involved in anthocyanin synthesis. Compared with green 'Anjou', the shaded peel of red 'Anjou' had higher anthocyanin concentrations, higher transcript levels of MYB10 and higher activity of UDP-glucose:flavonoid 3-O-glycosyltransferase (UFGT), suggesting that MYB10 regulates UFGT to control anthocyanin synthesis in red 'Anjou' peel. In the sun-exposed peel, activities of phenylalanine ammonia lyase, dihydroflavonol reductase, flavonol synthase and anthocyanidin synthase as well as UFGT were higher in red 'Anjou' than in green 'Anjou'. The peel of red 'Anjou' had higher activities of sorbitol dehydrogenase, raffinose synthase and sucrose synthase and higher levels of raffinose, myo-inositol and starch, indicating that sorbitol metabolism, raffinose synthesis and starch synthesis were upregulated in red 'Anjou'. The flesh of red 'Anjou' had higher concentrations of glucose, but lower activities of ATP-dependent phosphofructokinase, pyruvate kinase and glucose-6-phosphate dehydrogenase and lower dark respiration. The peel of red 'Anjou' had higher activities of glutaminase, asparagine synthetase and asparaginase, and higher concentrations of asparagine, aspartate, alanine, valine, threonine and isoleucine. The effects of anthocyanin synthesis on primary metabolism in fruit peel are discussed.

Cloning and bioinformatic analysis of transcription factor MYB10 from the red-leaf peach

“…Certain studies of factors regulating anthocyanin biosynthesis have demonstrated that the protein AN2 plays an important role in determining petunia coloration (Boase et al, 2015), and that AtPAP1 and AtPAP2 regulate anthocyanin accumulation in Arabidopsis thaliana stems and leaves (Borevitz et al, 2000;Li et al, 2014). In the grapevine, VvMybA controls anthocyanin biosynthesis by modulating UFGT expression (Kobayashi et al, 2002;Dong et al, 2015).…”

“…However, the MYB transcription factor-regulatory mechanism remains far from clear. For example, most MYB genes positively regulate anthocyanin accumulation (Chagné et al, 2013;Li et al, 2014;Lin-Wang et al, 2014), although a small number function as negative regulators (Aharoni et al, 2001;Yang et al, 2015). The transcription factor R2R3-MYB has many regulatory modes in anthocyanin biosynthesis (Wang et al, 2004;Yang et al, 2015).…”

Reactive oxygen species produced via plasma membrane NADPH oxidase regulate anthocyanin synthesis in apple peel

“…In apple fruit, it was reported that MdMYB10 might control both skin color and anthocyanin accumulation in fruit flesh in certain apple genotypes, whereas MdMYB1 and MdMYBA were expressed in red sections of fruit skin in other genotypes (Takos et al 2006;Ban et al 2007;Espley et al 2007Espley et al , 2009). Compared to that of non-red fruits, red apple and pear fruit peels showed higher levels of MYB transcription (Takos et al 2006;Ban et al 2007;Feng et al 2010;Lin-Wang et al 2011;Li et al 2014). In these fruits, the regulation of anthocyanin synthesis by MYB was mainly correlated with UDP-glycose:flavonoid 3-O-glycosyltransferase (UFGT), an enzyme which catalyzes the final step of anthocyanin synthesis.…”

“…Other enzymes such as phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), chalcone-flavanone isomerase (CHI), flavanone-3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS) are also involved in the synthesis of anthocyanin in apple or pear peels . MYB (MdMYB1, PyMYB10, and MdMYBA) and UFGT levels, UFGT activity, and anthocyanin concentration can be enhanced by sunlight (Takos et al 2006;Li et al , 2012Li et al , 2013aLi et al , 2014Yu et al 2012) or UV irradiation (Ubi et al 2006;Ban et al 2007;Xie et al 2012) in apple or pear peels, indicating that anthocyanin synthesis is regulated by light. However, the mechanisms underlying sunlight-mediated MYB and anthocyanin synthesis are unknown.…”

“…Moreover, the activity of plasma membrane NADPH oxidase can be enhanced by UV-B irradiation (Tossi et al 2009). Because the photosynthetic capacity of fruit peels is very low (Chen and Cheng 2007;Li et al 2014), ROS may be largely produced in peel chloroplasts. Mubarakshina et al (2010) suggest that ROS produced in chloroplasts, such as hydrogen peroxide, can also serve as signaling molecules.…”