Qifeng Zhao

Organic acids are the core of fruit flavor quality and cell metabolism, but a comprehensive review of their metabolism and regulatory networks in fruit trees is still limited. Here, we systematically summarized the biosynthesis, degradation and transport of major organic acids in fruits of horticultural crops. We focused on the distribution and molecular regulation of organic acids in citrus, pome fruits, stone fruits, grapes and tropical–subtropical fruits, and emphasized the regulation of transcription factors, epigenetic modifications and environmental signals. We also evaluated the progress of various omics strategies for dissecting organic acid metabolism and identifying key regulatory genes. Finally, we discuss the current research gaps and propose future directions for multi-gene editing and molecular design breeding. This review provides a theoretical framework for improving fruit flavor quality and breeding excellent varieties.

Downy mildew caused by Plasmopara viticola seriously affects global grape production. In this study, the cultivars of Moldova and Red Globe were inoculated with Plasmopara viticola separately. The results showed that the inoculated sites on Red Globe leaves were densely covered with white cotton-like mycelial mats, whereas sparse white mycelia were observed on Moldova leaves. Disease index analysis of Moldova and Red Globe after inoculation with the pathogen showed that Red Globe had a much higher disease index than Moldova, indicating that Red Globe was a highly resistant cultivar, while Moldova was a susceptible cultivar. Furthermore, it was discovered that Moldova had significantly higher contents of lignin, total phenols, and flavonoids than Red Globe. Moreover, RNA-seq technology was used to analyze transcriptomic changes in Red Globe and Moldova after inoculation at 1 dpi and 5 dpi separately. Combined with GO and KEGG databases to annotate differentially expressed genes (DEGs), the DEGs related to the plant hormone signal transduction pathway ( VvPR1, VvJAR1, VvSUC11 , etc.), phenylpropanoid metabolism ( VvCAD, VvCCoAOMT , etc.), flavonoid biosynthesis pathways ( VvCHS, VvF3H, VvDFR , etc.), and the stilbenoid, diarylheptanoid, and gingerol biosynthesis pathway ( VvROMT, VvSTSs ) were further analyzed. Furthermore, the results showed that Moldova activated more disease-resistant genes in the phenylpropanoid metabolic pathway, and the expression levels of genes related to disease-resistant pathways were significantly higher than those in Red Globe. This study lays a foundation for screening candidate target genes for downy mildew-resistant grape breeding and for analyzing the interaction mechanism between the pathogen and grapes.

Drought ranks among the key abiotic stresses that limit the growth and yield of grapevines (Vitis vinifera L.). Flavonols, a class of antioxidants commonly found in grapevines, play a crucial role in combating drought stress. In this study, we characterized the function and regulatory mechanism of the grapevine VviMYC4 in mediating flavonol biosynthesis in response to drought stress. VviMYC4 encodes a protein of 468 amino acids with conserved bHLH-MYC_N and bHLH domains. Phylogenetic analysis confirmed its homology with the grapevine VviMYC2 and similarity in function. The expression of VviMYC4 in ‘Cabernet Sauvignon’ grapevine seedling leaves increased initially and then decreased during prolonged drought stress. The homologous and heterologous transformation of VviMYC4 in grape suspension cells, Arabidopsis plants, tobacco leaves, and grapevine leaves demonstrated its ability to positively regulate flavonol biosynthesis and accumulation by promoting the expression of flavonol-related genes, thereby enhancing the drought tolerance of transgenic plants. Furthermore, VviMYC4 could bind to specific E-box sites on the promoters of VviF3H and VviFLS to improve their activities. This study highlights VviMYC4 as a pivotal positive regulator of drought tolerance in grapevines and proposes that VviMYC4 enhances the antioxidant and reactive oxygen species (ROS) scavenging abilities of grapevines in challenging environments and improves their stress resilience by mediating flavonol biosynthesis. Our findings offer crucial candidate genes and valuable insights for the molecular breeding of grapevine drought resistance.

The aroma metabolites in grape berries have received attention in recent years, but a global analysis of gene-regulated metabolites is still lacking. In this study, three grape cultivars, “Kyoho”, “Adenauer Rose”, and “Mei Xiangbao”, were used to determine the differential accumulation of metabolites and identify candidate genes related to grape berry aroma. A total of 27,228 genes were detected from the transcriptome, and 128 differentially accumulated metabolites (DAMs) were identified. Terpenoids and ester were the major substances in these three cultivars. KEGG enrichment showed that 12, 8, and 5 compounds were significantly enriched during the maturation process of these three grape cultivars, with most being terpenoids. A combined transcriptome and metabolome analysis found that the associated genes and metabolites were enriched in the following pathways: “Glycine, serine, and threonine metabolism”, “Cysteine and methionine metabolism”, “Tyrosine metabolism”, “Phenylalanine metabolism”, and “Phenylalanine, tyrosine, and tryptophan biosynthesis”. Seven structural genes (VvOMR1, VvGLYK, VvLPD2, VvAK2, VvSHM7, VvASP3, and VvASP1) and four transcription factors (VvERF053, VvERF4, VvMYB46, and VvMYB340) related to grape berry aroma accumulation were discovered. Our findings provide new insights into grape aroma formation and regulatory mechanism research, and the results will be beneficial for grape aroma breeding in the future.

Scattered light can make the distribution of light in plant canopies more uniform. In this study, Vitis vinifera L. ‘Wuhe Cuibao’ fresh grapes was used as the test material, and open field cultivation was used as a control. The diurnal variation of light intensity under different materials of rain shelter film was studied to compare the effects of rain shelter film on photosynthetic characteristics, disease resistance, and fruit quality of grape leaves. The results showed that the light intensity under DL (diffuse light) film on the west side at noon was significantly higher than that under outdoor cultivation and EVA (ethylene vinyl acetate) film coverage. The daily average net photosynthetic rate of grape leaves covered with DL film on the east side is higher than that of open cultivation and EVA film covering. The incidence rate of leaf Downy mildew could be reduced by different materials of rain covering film, but the difference was not significant. Covering DL film can significantly increase the increase rate of soluble sugar and accelerate the decrease of titratable acid content in the west side. The content of VC (vitamin C)) in the eastern fruit under DL film was significantly higher than that of the control, and the total phenolic content in the fruit under DL film was significantly higher than that under EVA film. The DL film shelter can improve the light intensity, improve the photosynthetic capacity of grape leaves, and significantly improve fruit quality.

Sucrose is the end product of photosynthesis in plants. Sucrose phosphate synthase (SPS) is a plant enzyme involved in sucrose biosynthesis that plays a crucial role in sugar metabolism, plant growth and biomass accumulation. So far, SPS gene family in grape (Vitis vinifera) has not been described. In this study, the genome-wide identification and characterization of SPS genes (VviSPS) in grape were analyzed. The physical and chemical properties, gene structure, evolutionary relationship, conserved domains, protein structure prediction and expression analyses were performed. In the results, total 4 putative VviSPS genes were identified, all of which had similar characteristics in genome and peptide sequences. Meanwhile, the four VviSPS genes also showed similar expression patterns in different tissues. They were mainly active in leaves and pulps, especially in mature leaves and early pulps. In conclusion, these results would provide a reference for the VviSPS gene function analysis in the future.