Mining of candidate genes for grape berry cracking using a genome-wide association study

Fruit cracking is a common phenomenon during the growth and development of horticultural crops that seriously affects fruit yield and quality.However,there are few studies on the mining of candidate genes related to berry cracking.To better understand the genetic basis of grape berry cracking,we conducted a genome-wide association study(GWAS)of grape varieties.Based on the mixed linear model(MLM),we detected five single nucleotide polymorphism(SNP)loci associated with berry-cracking index and two SNP loci associated with berry-cracking type in two years.These loci were mainly distributed on four chromosomes,namely 1,2,3,and 18,and were associated with ten unique candidate berry-cracking genes.The gene expression patterns indicated that the candidate genes in the susceptible berrycracking variety were more abundant than in the resistant berry-cracking variety.Grape berry-cracking is a complex trait controlled by multiple genes,mainly including genes involved in polygalacturonase,copper transporter,and receptor-like proteins.The high expression of the candidate berry-cracking genes may promote the occurrence of berry cracking,so the present study helps to further elucidate the genetic mechanism of berry cracking.

Control of ovule development in Vitis vinifera by VvMADS28 and interacting genes

Seedless grapes are increasingly popular throughout the world,and the development of seedless varieties is a major breeding goal.In this study,we demonstrate an essential role for the grapevine MADS-box gene VvMADS28 in morphogenesis of the ovule.We found that VvMADS28 mRNA accumulated in the ovules of a seeded cultivar,‘Red Globe’,throughout the course of ovule and seed development,especially within the integument/seed coat.In contrast,in the seedless cultivar‘Thompson Seedless’,VvMADS28 was expressed only weakly in ovules,and this was associated with increased levels of histone H3 lysine 27 trimethylation(H3K27me3)within the VvMADS28 promoter region.RNAi-mediated transient suppression of VvMADS28 expression in‘Red Globe’led to reduced seed size associated with inhibition of episperm and endosperm cell development.Heterologous overexpression of VvMADS28 in transgenic tomatoes interfered with sepal development and resulted in smaller fruit but did not obviously affect seed size.Assays in yeast cells showed that VvMADS28 is subject to regulation by the transcription factor VvERF98,and that VvMADS28 could interact with the Type I/MβMADS-domain protein VvMADS5.Moreover,through DNA-affinity purification-sequencing(DAP-seq),we found that VvMADS28 protein specifically binds to the promoter of the grapevine WUSCHEL(VvWUS)gene,suggesting that maintenance of the VvMADS28–VvMADS5 dimer and VvWUS expression homeostasis influences seed development.Taken together,our results provide insight into regulatory mechanisms of ovule and seed development associated with VvMADS28.

Physiological Response to High Temperature and Evaluation of Heat Tolerance of Different Grape Cultivars

[Objectives]This study was conducted to investigate the differences in the physiological responses of different grape cultivars to high temperature.[Methods]The 19 tested cultivars were selected from the grape germplasm resources pool of Turpan Research Institute of Xinjiang Academy of Agricultural Sciences.Twelve physiological indexes including gas exchange parameters,chlorophyll content,antioxidant enzyme activity and proline content were determined in grape leaves under field conditions during the middle period of local natural high temperature period(July,daily maximum air temperature>35℃).The heat tolerance of different cultivars was evaluated by fuzzy membership function analysis and optimum partitioning clustering of ordered samples.[Results](1)Under natural high temperature conditions in Turpan,the 19 tested grape cultivars responded differently to high temperature.‘Red Globe’,‘Fujiminori’,‘Beta’,‘Hetianhuang’had strong heat tolerance,while‘Thompson Seedless’,‘Hongqi Tezaomeigui’,‘Shuijing Wuhe’,‘Victoria’,‘Yatomi Rosa’and‘Crimson Seedless’had weak heat tolerance.(2)Among the 12 physiological indexes,malondialdehyde content and antioxidant enzyme activity were mostly different among various grape cultivars.The grape cultivars with strong heat tolerance,‘Red Globe’and‘Fujiminori’,had relatively lower malondialdehyde contents,while‘Beta’and‘Hetianhuang’had relatively higher malondialdehyde contents.But they had higher activity of antioxidant enzymes.(3)The results of fuzzy membership function analysis showed that the cumulative membership value(AR)of each physiological index was consistent with its apparent heat tolerance performance,suggesting that AR can be a potential index for the evaluation of heat tolerance of grape cultivars.Further cluster analysis classified the tested cultivars as strong,medium and weak.‘Red Globe’,‘Fujiminori’,‘Beta’and‘Hetianhuang’had strong heat tolerance.[Conclusions]This study provides a reference for grape cultivation under high temperature and stress and breeding of heat-tolerant varieties.