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Grape is an economically important crop but recalcitrant to Agrobacterium-mediated genetic transformation and in vitro regeneration. Here, we have developed a protocol for transient transformation of grapes by investigating the effects of explant pre-culture and duration of vacuum infiltration on transformation efficiency. Using sliced grape berries of "Shine-Muscat" (Vitis labrusca × Vitis vinifera) between the end of fruit expansion phase and the mature stage as explants, we firstly compared the effect of pre-culture explants into a susceptible state (incubation on Murashige and Skoog (MS) agar plate in the dark at 25 ± 1 °C for 48 h) with no pre-culture and then tested different vacuum infiltration times on transformation efficiency using β-glucuronidase (GUS) reporter system. Pre-culture increased the susceptibility of explants to the agrobacteria infection and increased transient transformation efficiency as assessed by histochemical GUS activity, with intense blue coloration compared with the faint staining observed in the non-susceptible explants. Using a Circulating Water Vacuum Pump system to facilitate agrobacteria entry into berry cells, we tested vacuum durations of 5, 10, and 15 min and observed that transformation efficiency increased with vacuum duration of infiltration. These results were confirmed by relative gene expression of GUS transgene as assessed by RT-qPCR and GUS activity assay. To further confirm the usefulness of our protocol, we transiently transformed grape berries with the hydrogen peroxide sensor gene VvHPCA3, and this was confirmed by gene expression analysis as well as increased sensitivity of the explants to hydrogen peroxide treatment. Overall, this study has resulted in a simple but efficient transient transformation protocol for grape berries and would be a valuable tool for the rapid testing of gene function and the study of key regulatory networks in this important crop. [ABSTRACT FROM AUTHOR]

Background: 5-Azacytidine (5-azaC) promotes the development of 'Kyoho' grape berry but the associated changes in gene expression have not been reported. In this study, we performed transcriptome analysis of grape berry at five developmental stages after 5-azaC treatment to elucidate the gene expression networks controlling berry ripening. Results: The expression patterns of most genes across the time series were similar between the 5-azaC treatment and control groups. The number of differentially expressed genes (DEGs) at a given developmental stage ranged from 9 (A3_C3) to 690 (A5_C5). The results indicated that 5-azaC treatment had not very great influences on the expressions of most genes. Functional annotation of the DEGs revealed that they were mainly related to fruit softening, photosynthesis, protein phosphorylation, and heat stress. Eight modules showed high correlation with specific developmental stages and hub genes such as PEROXIDASE 4, CAFFEIC ACID 3-O-METHYLTRANSFERASE 1, and HISTONE-LYSINE N-METHYLTRANSFERASE EZA1 were identified by weighted gene correlation network analysis. Conclusions: 5-AzaC treatment alters the transcriptional profile of grape berry at different stages of development, which may involve changes in DNA methylation. [ABSTRACT FROM AUTHOR]

Background: In a previous study, the early ripening of Kyoho grape following H2O2 treatment was explored at the physiological level, but the mechanism by which H2O2 promotes ripening at the molecular level is unclear. To reveal the molecular mechanism, RNA-sequencing analysis was conducted on the different developmental stages of Kyoho berry treated with H2O2. Results: In the comparison of treatment and control groups, 406 genes were up-regulated and 683 were down-regulated. Time course sequencing (TCseq) analysis showed that the expression patterns of most of the genes were similar between the treatment and control, except for some genes related to chlorophyll binding and photosynthesis. Differential expression analysis and the weighted gene co-expression network were used to screen significantly differentially expressed genes and hub genes associated with oxidative stress (heat shock protein, HSP), cell wall deacetylation (GDSL esterase/lipase, GDSL), cell wall degradation (xyloglucan endotransglucosylase/ hydrolase, XTH), and photosynthesis (chlorophyll a-b binding protein, CAB1). Gene expression was verified with RT-qPCR, and the results were largely consistent with those of RNA sequencing. Conclusions: The RNA-sequencing analysis indicated that H2O2 treatment promoted the early ripening of Kyoho berry by affecting the expression levels of HSP, GDSL, XTH, and CAB1 and- photosynthesis- pathways. [ABSTRACT FROM AUTHOR]

Previous study has demonstrated that the riboflavin treatment promoted the early ripening of the 'Kyoho' grape berry. However, the molecular mechanism causing this was unclear. In order to reveal the regulation mechanism of riboflavin treatment on grape berry development and ripening, the different berry developmental stages of the 'Kyoho' berry treated with 0.5 mmol/L of riboflavin was sampled for transcriptome profiling. RNA-seq revealed that 1526 and 430 genes were up-regulated and down-regulated, respectively, for the comparisons of the treatment to the control. TCseq analysis showed that the expression patterns of most of the genes were similar between the treatment and the control, except for some genes that were related to the chlorophyll metabolism, photosynthesis–antenna proteins, and photosynthesis, which were revealed by the enrichment analysis of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). The differentially expressed genes and weighted gene co-expression network analysis (WGCNA) analysis identified some significantly differentially expressed genes and some hub genes, including up-regulation of the photosynthesis-related ELIP1 and growth and development-related GDSL; and down-regulation of the oxidative stress-related ATHSP22 and berry softening-related XTH32 and GH9B15. The results suggested that the riboflavin treatment resulted in the variations of the expression levels of these genes, and then led to the early ripening of the 'Kyoho' berry. [ABSTRACT FROM AUTHOR]

Grape (Vitis vinifera L.) berries are susceptible to quality deterioration after harvest. This study aimed to investigate the effect of folic acid (FA) treatment on the postharvest quality of table grape berries. Harvested 'Kyoho' (V. vinifera × V. labrusca L.) bunches were immersed in 1 mg L−1 FA solution for 15 min, then stored for sample collection and phenotype observation. Treatment with FA decreased the rates of berry abscission, water loss, and berry softening, reduced the accumulation of reactive oxygen species (ROS), and altered ROS metabolism-associated enzyme activities and gene expression levels. Transcriptome analysis revealed 507, 684, and 250 differentially expressed genes (DEGs) between FA-treated and non-treated berries at 3, 6, and 9 d after treatment, respectively. The DEGs were grouped into six modules according to a weighted correlation network analysis. A hub transcription factor, annotated as a WRKY transcription factor, was screened from the module associated with cell wall metabolism and identified as VvWRKY31. Transient transformation of grape berry slices revealed that overexpression of VvWRKY31 enhanced the relative expression level of VvRboh. The dual-luciferase assay showed that VvWRKY31 was capable of binding to VvRboh promoter. The present results provide insights into the potential molecular mechanism underlying FA-induced delay postharvest quality deterioration of grape berries. Specifically, FA inhibits expression of genes associated with ROS generation by reducing VvWRKY31 expression, thereby delaying quality deterioration induced by excessive accumulation of ROS. These results will be helpful in table grape breeding programs focused on delaying deterioration in postharvest quality. • Folic acid affects ROS metabolism in postharvest grape. • VvWRKY31 is a hub transcription factor in cell wall metabolism. • VvWRKY31 promotes VvRboh expression by binding its promoter. [ABSTRACT FROM AUTHOR]