Expression of genes involved in the anthocyanin biosynthesis pathway in white and red fruits of Fragaria pentaphylla and genetic variation in the dihydroflavonol-4-reductase gene

Mutations in PmUFGT3 contribute to color variation of fruit skin in Japanese apricot (Prunus mume Sieb. et Zucc.)

BACKGROUND

Japanese apricot (Prunus mume Sieb. et Zucc.) is popular for both ornamental and processing value, fruit color affects the processing quality, and red pigmentation is the most obvious phenotype associated with fruit color variation in Japanese apricot, mutations in structural genes in the anthocyanin pathway can disrupt the red pigmentation, while the formation mechanism of the red color trait in Japanese apricot is still unclear.  RESULTS: One SNP marker (PmuSNP_27) located within PmUFGT3 gene coding region was found highly polymorphic among 44 different fruit skin color cultivars and relative to anthocyanin biosynthesis in Japanese apricot. Meantime, critical mutations were identified in two alleles of PmUFGT3 in the green-skinned type is inactivated by seven nonsense mutations in the coding region, which leads to seven amino acid substitution, resulting in an inactive UFGT enzyme. Overexpression of the PmUFGT3 allele from red-skinned Japanese apricot in green-skinned fruit lines resulted in greater anthocyanin accumulation in fruit skin. Expression of same allele in an Arabidopsis T-DNA mutant deficient in anthocyanidin activity the accumulation of anthocyanins. In addition, using site-directed mutagenesis, we created a single-base substitution mutation (G to T) of PmUFGT3 isolated from green-skinned cultivar, which caused an E to D amino acid substitution and restored the function of the inactive allele of PmUFGT3 from a green-skinned individual.

CONCLUSION

This study confirms the function of PmUFGT3, and provides insight into the mechanism underlying fruit color determination in Japanese apricot, and possible approaches towards genetic engineering of fruit color.

Integrated metabolomic and transcriptomic analysis reveals factors underlying differences in fruit quality between Fragaria nilgerrensis and Fragaria pentaphylla

BACKGROUND

Strawberries have become one of the most popular fruits because of their unique flavor and high nutritional value. Fruit quality and price are the most important criteria that determine consumer acceptability. Fragaria nilgerrensis and Fragaria pentaphylla are two wild Asian diploid strawberry species that differ in fruit color, taste, and aroma. To understand the molecular mechanisms involved in the formation of high-quality strawberry fruit, we integrated transcriptomics and metabolomics research methods to compare the metabolic and biosynthetic mechanisms of the two Fragaria species.

RESULTS

F. nilgerrensis fruit has higher amino acid and lipid contents and a higher sugar-to-acid ratio than F. pentaphylla fruit does, underlying their superior nutritional value, aroma, firmness, and taste. Compared with F. nilgerrensis fruit, F. pentaphylla fruit contained more flavonoids, indicating its enhanced color and health benefits. In addition, candidate structural genes that regulate the biosynthesis of flavonoids, amino acids, and glycerophospholipids in the two strawberry fruit were screened.

CONCLUSIONS

The differences in aroma, firmness, and taste between F. nilgerrensis fruit and F. pentaphylla fruit are probably due to differences in their amino acid and lipid contents, as well as the difference in their sugar-to-acid ratios. Eight key structural genes that may play important roles in the biosynthesis of amino acids, lipids, and flavonoids were identified. © 2021 Society of Chemical Industry.

Expression of Structural Flavonoid Biosynthesis Genes in Dark-Blue and White Myrtle Berries (Myrtus communis L.)

Within the myrtle (Myrtus communis L.) species, different genotypes may produce dark-blue berries or white berries depending on the peel color upon ripening. One dark-blue cultivar and one white myrtle cultivar were used to study the molecular mechanisms underlying flavonoid biosynthesis. The relative expression levels of common (PAL, CHS, CHI, DFR and LDOX) and specific (FLS, ANR, LAR and UFGT) flavonoid genes were analyzed during fruit development by means of quantitative real-time polymerase chain reaction (RT-qPCR). Moreover, the anthocyanin content was determined, and it showed an increase with the ripening of the berries of the dark-blue cultivar. The results showed an increased transcript abundance of PAL, CHI, DFR, LDOX and UFGT gene expression in the dark-blue cultivar compared to the white one, as well as a strong positive correlation between the changes in gene expression and anthocyanin accumulation. The transcript levels of UFGT showed sharp increases at 150 and 180 days after full blooming (DAF) in the dark-blue cultivar, which corresponded with anthocyanin accumulation. However, ripening seemed to modulate the expression of genes implicated in flavonols (i.e., FLS) and flavan-3-ols (i.e., LAR and ANR) in different manners. However, whereas FLS transcript accumulation increased at the end of the ripening period in the dark-blue cultivar, LAR and ANR gene expression decreased in both cultivars.

Developmental Variation in Fruit Polyphenol Content and Related Gene Expression of a Red-Fruited versus a White-Fruited Fragaria vesca Genotype

Two cultivars of F. vesca, red-fruited Baron Solemacher (BS) and white-fruited Pineapple Crush (PC), were studied to compare and contrast the quantitative accumulation of major polyphenols and related biosynthetic pathway gene expression patterns during fruit development and ripening. Developing PC fruit showed higher levels of hydroxycinnamic acids in green stages and a greater accumulation of ellagitannins in ripe fruit in comparison to BS. In addition to anthocyanin, red BS fruit had greater levels of flavan-3-ols when ripe than PC. Expression patterns of key structural genes and transcription factors of the phenylpropanoid/flavonoid biosynthetic pathway, an abscisic acid (ABA) biosynthetic gene, and a putative ABA receptor gene that may regulate the pathway, were also analyzed during fruit development and ripening to determine which genes exhibited differences in expression and when such differences were first evident. Expression of all pathway genes differed between the red BS and white PC at one or more times during development, most notably at ripening when phenylalanine ammonia lyase 1 (PAL1), chalcone synthase (CHS), flavanone-3′-hydroxylase (F3′H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and UDP:flavonoid-O-glucosyltransferase 1 (UFGT1) were significantly upregulated in the red BS fruit. The transcription factors MYB1 and MYB10 did not differ substantially between red and white fruit except at ripening, when both the putative repressor MYB1 and promoter MYB10 were upregulated in red BS but not white PC fruit. The expression of ABA-related gene 9-cis-epoxycarotenoid dioxygenase 1 (NCED1) was higher in red BS fruit but only in the early green stages of development. Thus, a multigenic effect at several points in the phenylpropanoid/flavonoid biosynthetic pathway due to lack of MYB10 upregulation may have resulted in white PC fruit.

Metabolic Flux Enhancement and Transcriptomic Analysis Displayed the Changes of Catechins Following Long-Term Pruning in Tea Trees ( Camellia sinensis)

The tea tree is a perennial woody plant, and pruning is one of the most crucial cultivation measurements for tea plantation management. To date, the relationship between long-term pruning and metabolic flux enhancement in tea trees has not been studied. In this research, 11-year-old pruned tea trees from four different cultivars were randomly selected for transcriptome analysis and characteristic secondary metabolite analysis together with controls. The findings revealed that epigallocatechin gallate (EGCG) accumulation in pruned tea trees was significantly higher than that in unpruned tea trees. SCPL1A expression (encoding a class of serine carboxypeptidase), which has been reported to have a catalytic ability during EGCG biosynthesis, together with LAR, encoding leucoanthocyanidin reductase, was upregulated in the pruned tea trees. Moreover, metabolic flux enhancement and transcriptome analysis revealed low EGCG accumulation in the leaves of unpruned tea trees. Because of the bitter and astringent taste of EGCG, these results provide a certain understanding to the lower bitterness and astringency in teas from "ancient tea trees", growing in the wild with no trimming, than teas produced from pruned plantation trees.

Transcriptome sequencing of Paeonia suffruticosa 'Shima Nishiki' to identify differentially expressed genes mediating double-color formation

Paeonia suffruticosa 'Shima Nishiki' is one of extremely rare double-color cultivars in the world. It usually shows the two beautiful colors of red and white in the same flower, and this trait undoubtedly makes the flowers more charming for the ornamental market. However, few studies have been done to unravel the molecular mechanisms of double-color formation in P. suffruticosa 'Shima Nishiki'. In this study, we measured the anthocyanin composition and concentration, and sequenced the transcriptomes of the red and white petals. We found that the total content of Pg-based glycosides was at a significantly higher level in the red petals. Furthermore, we assembled and annotated 92,671 unigenes. Comparative analyses of the two transcriptomes showed 227 differentially expressed genes (DEGs), among which 57 were up-regulated, and 170 were down-regulated in the red petals. Subsequently, we identified 3 DEGs and the other 6 structural genes in the anthocyanin biosynthetic pathway including PsCHS, PsCHI, PsF3H, PsF3'H, PsDFR, PsANS, PsAOMT, PsMYB, and PsWD40. Among them, PsDFR and PsMYB expressed at a significantly higher level and showed positive correlations between their expression and anthocyanin concentration in the red petals. However, PsWD40 expressed at a significantly lower level and exhibited an inverse relationship in the red petals. Furthermore, we further confirmed the relative expression of the 9 candidate genes using quantitative real-time PCR. Based on the above results, we concluded that the significant differential expression of PsDFR, PsMYB and PsWD40 may play a key role in anthocyanin concentration in the red and white petals, thereby mediating double-color formation. These data will provide a valuable resource to better understand the molecular mechanisms of double-color formation of P. suffruticosa 'Shima Nishiki'.