Variances In Flavonoid Biosynthesis Profiles Between ’Zaosu’ Pear And Its Red Mutant With The Genes Involved

To determine the flavonoid biosynthesis pattern in ‘Zaosu’pear and its red mutant, theflavonoid compounds in the fruits peel which were treated by different re-exposure durationwere qualified and quantified by HPLC. A biosynthesis interaction forecasting model ofdifferential flavonoid compounds was set up by stepwise linear regression and partialcorrelation. Moreover, as the key enzyme in the distinct pathway between ‘Zaosu’ pear and itsred mutant, UFGalT has been identified and its coding gene was isolated from the peargenome.1. By bagging and differential duration re-exposing, we obtained a gradient of pear fruitswhose peel color from light yellow to dark red. The characteristic biosynthesis patterns of allmajor flavonoid compounds in ‘Zaosu’ and its red mutant were demonstrated by qualified andquantified16kinds of flavonoid compounds in these materials.2.In ‘Zaosu’ pear, the synthesis pattern of each flavonoid compounds was relativelyindependent, and two distinct flavonoid3-glycosides synthesis patterns were identified by thecorrelation analysis: the biosynthesis of flavonoid3-galactosides/arabinosides was suppressedand barely affected by bagging or re-exposing treatments, but other kinds of flavonoid3-glycosides (gluctosides/rutinosides) gradually re-accumulated when they re-exposed to thesunlight, which were similar with the synthesis pattern in the red mutant. In the red mutant,the biosynthesis patterns of all flavonoid compounds were highly correlated, except forarbutin and phenolic acids, which were hardly affected by the bagging or re-exposingtreatments.3. A combination of correlation,multicollinearity test and partial-correlation analysesamong major flavonoid metabolites indicated that biosynthesis of eachphenolic compoundwas independent in ‘Zaosu’ pear, except for the positive correlation between flavonoid3-rutincosidesand flavanols. In contrast with the green pear cultivar, almost all phenoliccompounds in the red mutant had similarbiosynthesis patterns except for arbutin. However,only the biosynthesis of flavonoid3-galactosides was relativelyindependent and stronglyaffected the synthesis of the other phenolic compounds. Therefore, we propose a hypothesisthatthe strong accumulation of flavonoid3-galactosides stimulated the biosynthesis of other flavonoid compounds in the redmutant and, therefore, caused systemic variation of flavonoidbiosynthesis profiles between ‘Zaosu’ and its red mutant.4.Thishypothesis had been further demonstrated by the enzyme activity of UFGalT, andtranscript levels of flavonoid biosyntheticgenes：the expression pattern of PbUFGT1,whichencoding UFGalT, was highly sensitive to the sunlight in the red mutant but barely activatedin ‘Zaosu’ pear, the enzyme activity of UFGalT showed the similar trends with its geneexpression pattern in the both cultivars.