Cit1,2RhaT and two novel CitdGlcTs participate in flavor-related flavonoid metabolism during citrus fruit development

Abstract

Neohesperidosides are disaccharides that are present in some flavonoids and impart a bitter taste, which can significantly affect the commercial value of citrus fruits. In this study, we identified three flavonoid-7- O - di -glucosyltransferase ( dGlcT ) genes closely related to 1,2-rhamnosyltransferase ( 1,2RhaT ) in citrus genomes. However, only 1,2RhaT was directly linked to the accumulation of neohesperidoside, as demonstrated by association analysis of 50 accessions and co-segregation analysis of an F 1 population derived from Citrus reticulata × Poncirus trifoliata . In transgenic tobacco BY2 cells, over-expression of CitdGlcT s resulted in flavonoid-7- O -glucosides being catalysed into bitterless flavonoid-7- O - di -glucosides, whereas over-expression of Cit1,2RhaT converted the same substrate into bitter-tasting flavonoid-7- O -neohesperidoside. Unlike 1,2RhaT , during citrus fruit development the dGlcT s showed an opposite expression pattern to CHS and CHI , two genes encoding rate-limiting enzymes of flavonoid biosynthesis. An uncoupled availability of dGlcTs and substrates might result in trace accumulation of flavonoid-7- O - di -glucosides in the fruit of C. maxima (pummelo). Past human selection of the deletion and functional mutation of 1,2RhaT has led step-by-step to the evolution of the flavor-related metabolic network in citrus. Our research provides the basis for potentially improving the taste in citrus fruit through manipulation of the network by knocking-out 1,2RhaT or by enhancing the expression of dGlcT using genetic transformation.

Genome-wide characterization, evolution and expression profiling of UDP-glycosyltransferase family in pomelo (Citrus grandis) fruit

“…Several UGT genes have been functionally characterized in plants, such as Arabidopsis thaliana [5], Zea mays [18], Triticum aestivum [26], Brassica rapa [27] and Prunus persica [20]. In citrus, only three UGTs have been functionally identi ed, Cm1_2RhaT from pomelo, Cs1,6RhaT and CsUGT76F1 from sweet orange associated with avonoid glycosylation [13][14][15][16], and three putative terpenoid UGTs, CsUGT1, CsUGT2 and CsUGT3 [17]. However, no large-scale analysis was found in citrus.…”

“…All UGT members were divided into 16 phylogenetic groups, including 14 conservative groups (A-N) identi ed in Arabidopsis [2], and two newly identi ed groups O and P found in other plants, such as grapevine [5]. Cm1_2RhaT (100% amino acid sequence identity to Cg1g023820) from pomelo and Cs1,6RhaT from sweet orange that were identi ed as avonoid 7-O-UGTs [13,15,16], were clustered in group A. CsUGT76F1, located in group H, was identi ed as being involved in the biosynthesis of avonoid 7-O-glucosides and 7-O-rhamnosides in sweet orange [14]. Arabidopsis UGT73C6 ( avonol-3-O-rhamnoside-7-O-glucosyltransferase) [21] and strawberry FaGT7 ( avonol-3-O-glucosyltransferase) [8] were located in group D. Other UGTs responsible for avonol-3-O-glycosylation were located in group F, including UGT78D1 from Arabidopsis [22], and VvGT5 and VvGT6 from grapevine [7].…”

“…Among them, 13 UGTs (52%) belonged to group E, 10 UGTs (56% of members in group D) belonged to group D, 8 UGTs (47%) in group H, 9 UGTs (53%) in group I, and 7 UGTs (58%) in group L. The expression levels of 29 members in pomelo were highest at green stage (80 DAB), followed by 23 at color break stage (140 DAB), and 19 at mature stage (200 DAB). Cg1g023820 in group A had 100% identity with the amino acid sequence of Cm1_2RhaT from pomelo, which was identi ed to be a avonoid 7-O-UGT [13,15,16], showed the highest transcript levels at color break stage (140 DAB) and mature stage (200 DAB) in avedo of pomelo fruit. This nding was consistent with previous research.…”

Putative Synergetic Genes Involved in the Syntheses of Carotenoids and Flavonoids in 'Cara cara' Navel Orange as Revealed by Integrated Transcriptome and Metabolomics Analysis

“…Our previous study found that the contents of avonoids in four sweet oranges tended to be stable or slightly decreased during 90-210 DAF, and that the lycopene accumulation may have direct or indirect effects on the biosynthesis of avonoids [8]. The avonoids are synthesized from phenylpropanoid pathway, mainly including PAL, C4H, 4CL, CHS and CHI genes [30]. It was found that the expression levels of these genes were at high levels at 60 DFA, but simultaneously dropped to extremely low levels at 90 210 DAF in four pomelos, the key pathway genes might be regulated by some TFs [30].…”

“…The avonoids are synthesized from phenylpropanoid pathway, mainly including PAL, C4H, 4CL, CHS and CHI genes [30]. It was found that the expression levels of these genes were at high levels at 60 DFA, but simultaneously dropped to extremely low levels at 90 210 DAF in four pomelos, the key pathway genes might be regulated by some TFs [30]. Numerous TFs have been reported to regulate lignin and anthocyanin biosynthesis in phenylpropanoid pathway [31].…”