Berry color variation in grapevine as a source of diversity

Decoding the enhanced antioxidant activities of the combined small berry pomaces by widely targeted metabolomics analysis

Small berry pomaces (SBPs) are poorly utilized as an inexpensive source of bioactive compounds. This study investigated the impact of compounding treatment on nutritional and antioxidant characteristics of combined SBPs, in comparison with single SBP. The results showed that the amounts of protein, minerals, dietary fiber (DF) and anthocyanidins were significantly (p < 0.05) higher in combined SBPs than in combined fruits. Moreover, the combined SBPs were characterized by an elevated abundance of minerals and anthocyanidins (6 kinds, and 5 kinds, respectively), substantiating the effectiveness of compounding treatment on SBP nutrition. A total of 776 secondary phytochemicals were detected in combined SBPs by a widely targeted metabolomics approach. Each SBP contained approximately 100 kinds of unique natural antioxidants. Furthermore, the combined SBPs group had the highest antioxidant activity compared with single SBP. Meanwhile, the antioxidant activities determined in combined SBPs were higher than arithmetic mean value of single SBP. The synergism and interaction of active components in different sources of SBPs play vital role in the high antioxidant capacity of combined SBPs. All the results provide reference for the comprehensive development and utilization of fruit residues. The SBPs should be highly prized for their substantial amount of nutritional and bioactive constituents, including protein, DF, essential minerals and secondary metabolites. These secondary metabolites are positively associated with antioxidant benefits. The present study summarizes the knowledge about bioactive compounds and antioxidant activities of combined SBPs group and discusses the relevant mechanisms. A conclusion can be educed that combined process is an effective way to improve properties of the pomaces.

MYB24 orchestrates terpene and flavonol metabolism as light responses to anthocyanin depletion in variegated grape berries

Variegation is a rare type of mosaicism not fully studied in plants, especially fruits. We examined red and white sections of grape (Vitis vinifera cv. 'Béquignol') variegated berries and found that accumulation of products from branches of the phenylpropanoid and isoprenoid pathways showed an opposite tendency. Light-responsive flavonol and monoterpene levels increased in anthocyanin-depleted areas in correlation with increasing MYB24 expression. Cistrome analysis suggested that MYB24 binds to the promoters of 22 terpene synthase (TPS) genes, as well as 32 photosynthesis/light-related genes, including carotenoid pathway members, the flavonol regulator HY5 HOMOLOGUE (HYH), and other radiation response genes. Indeed, TPS35, TPS09, the carotenoid isomerase gene CRTISO2, and HYH were activated in the presence of MYB24 and MYC2. We suggest that MYB24 modulates ultraviolet and high-intensity visible light stress responses that include terpene and flavonol synthesis and potentially affects carotenoids. The MYB24 regulatory network is developmentally triggered after the onset of berry ripening, while the absence of anthocyanin sunscreens accelerates its activation, likely in a dose-dependent manner due to increased radiation exposure. Anthocyanins and flavonols in variegated berry skins act as effective sunscreens but for different wavelength ranges. The expression patterns of stress marker genes in red and white sections of 'Béquignol' berries strongly suggest that MYB24 promotes light stress amelioration but only partly succeeds during late ripening.

Transcriptome and metabolome reveal the effects of three canopy types on the flavonoids and phenolic acids in 'Merlot' (Vitis vinifera L.) berry pericarp

The flavonoids and phenolic acids in grape berries greatly influence the quality of wine. Various methods are used to shape and prune grapevines, but their effects on the flavonoids and phenolic acids remain unclear. The flavonoids and phenolic acids in the berry pericarps from grapevines pruned using three types of leaf canopy, namely, V-shaped, T-shaped, and vertical shoot-positioned (VSP) canopies, were compared in this study. Results showed that the V-shaped canopy was more favorable for the accumulation of flavonoids and phenolic acids. Transcriptome and metabolome analyses revealed that the differentially expressed genes (DEGs) and differentially regulated metabolites (DRMs) were significantly enriched in the flavonoid and phenylpropanoid biosynthesis pathways. A total of 96 flavonoids and 32 phenolic acids were detected among the DRMs. Their contents were higher in the V-shaped canopy than in the T-shaped and VSP canopies. Conjoint analysis of transcriptome and metabolome showed that nine DEGs (e.g., cytochrome P450 98A9 and 98A2) were significantly correlated to nine phenolic acids (e.g., gentisic acid and neochlorogenic acid) and three genes (i.e., chalcone isomerase, UDP-glycosyltransferase 88A1, and caffeoyl-CoA O-methyltransferase) significantly correlated to 15 flavonoids (e.g., baimaside and tricin-7-O-rutinoside). These genes may be involved in the regulation of various flavonoids and phenolic acids in grape berries, but their functions need validation. This study provides novel insights into the effects of leaf canopy on flavonoids and phenolic acids in the skin of grape berries and reveals the potential regulatory networks involved in this phenomenon.

Metabolite analysis reveals distinct spatio-temporal accumulation of anthocyanins in two teinturier variants of cv. 'Gamay' grapevines (Vitis vinifera L.)

White-fleshed grape cv. 'Gamay' and its two teinturier variants presented distinct spatial-temporal accumulation of anthocyanins, with uncoupled accumulation of sugars and anthocyanins in 'Gamay Fréaux'. In most red grape cultivars, anthocyanins accumulate exclusively in the berry skin, while 'teinturier' cultivars also accumulate anthocyanins in the pulp. Here, we investigated the teinturier cvs. 'Gamay de Bouze' and 'Gamay Fréaux' (two somatic variants of the white-fleshed cv. 'Gamay') through metabolic and transcript analysis to clarify whether these two somatic variants have the same anthocyanin accumulation pattern in the skin and pulp, and whether primary metabolites are also affected. The skin of the three cultivars and the pulp of 'Gamay de Bouze' begun to accumulate anthocyanins at the onset of berry ripening. However, the pulp of 'Gamay Fréaux' exhibited a distinct anthocyanin accumulation pattern, starting as early as fruit set with very low level of sugars. The highest level of anthocyanins was found in 'Gamay Fréaux' skin, followed by 'Gamay de Bouze' and 'Gamay'. Consistently, the transcript abundance of genes involved in anthocyanin biosynthesis were in line with the anthocyanin levels in the three cultivars. Despite no evident differences in pulp sugar content, the concentration of glucose and fructose in the skin of 'Gamay Fréaux' was only half of those in the skin of 'Gamay' and 'Gamay de Bouze' throughout all berry ripening, suggesting an uncoupled accumulation of sugars and anthocyanins in 'Gamay Fréaux'. The study provides a comprehensive view of metabolic consequences in grape somatic variants and the three almost isogenic genotypes can serve as ideal reagents to further uncover the mechanisms underlying the linkage between sugar and anthocyanin accumulation.

Mitotic gene conversion can be as important as meiotic conversion in driving genetic variability in plants and other species without early germline segregation

In contrast to common meiotic gene conversion, mitotic gene conversion, because it is so rare, is often ignored as a process influencing allelic diversity. We show that if there is a large enough number of premeiotic cell divisions, as seen in many organisms without early germline sequestration, such as plants, this is an unsafe position. From examination of 1.1 million rice plants, we determined that the rate of mitotic gene conversion events, per mitosis, is 2 orders of magnitude lower than the meiotic rate. However, owing to the large number of mitoses between zygote and gamete and because of long mitotic tract lengths, meiotic and mitotic gene conversion can be of approximately equivalent importance in terms of numbers of markers converted from zygote to gamete. This holds even if we assume a low number of premeiotic cell divisions (approximately 40) as witnessed in Arabidopsis. A low mitotic rate associated with long tracts is also seen in yeast, suggesting generality of results. For species with many mitoses between each meiotic event, mitotic gene conversion should not be overlooked.

Gene conversion associated with meiosis has long been a focus of attention in population genomics, but mitotic conversion has been relatively overlooked as it was thought to be rare. Analysis in plants suggests that this could be a mistake; long tract lengths and multiple mitoses in species lacking germline sequestration suggest that mitotic conversion, although rare per mitosis, should not be ignored.