A phylogenetic analysis of the grape genus (Vitis L.) reveals broad reticulation and concurrent diversification during neogene and quaternary climate change

Decoding the Chloroplast Genome of Tetrastigma (Vitaceae): Variations and Phylogenetic Selection Insights

Tetrastigma (Vitaceae) is known for its ornamental, medicinal, and ecological significance. However, the structural and variational characteristics of the Tetrastigma chloroplast genome and their impact on phylogenetic relationships remain underexplored. This study utilized bioinformatics methods to assemble and annotate the chloroplast genomes of 10 Tetrastigma species and compare them with five previously sequenced species. This study analyzed gene composition, simple sequence repeats, and codon usage patterns, revealing a high A/T content, uniquely identified pentanucleotide repeats in five species and several preferred codons. In addition, comparative analyses were conducted of the chloroplast genomes of 15 Tetrastigma species, examining their structural differences and identifying polymorphic hotspots (rps16, rps16-trnQ, trnS, trnD, psbC-trnS-psbZ, accD-psaI, psbE-petL-petG, etc.) suitable for DNA marker development. Furthermore, phylogenetic and selective pressure analyses were performed based on the chloroplast genomes of these 15 Tetrastigma species, validating and elucidating intra-genus relationships within Tetrastigma. Futhermore, several genes under positive selection, such as atpF and accD, were identified, shedding light on the adaptive evolution of Tetrastigma. Utilizing 40 Vitaceae species, the divergence time of Tetrastigma was estimated, clarifying the evolutionary relationships within Tetrastigma relative to other genera. The analysis revealed diverse divergences of Tetrastigma in the Miocene and Pliocene, with possible ancient divergence events before the Eocene. Furthermore, family-level selective pressure analysis identified key features distinguishing Tetrastigma from other genera, showing a higher degree of purifying selection. This research enriches the chloroplast genome data for Tetrastigma and offers new insights into species identification, phylogenetic analysis, and adaptive evolution, enhancing our understanding of the genetic diversity and evolutionary history of these species.

The wild side of grape genomics

With broad genetic diversity and as a source of key agronomic traits, wild grape species (Vitis spp.) are crucial to enhance viticulture's climatic resilience and sustainability. This review discusses how recent breakthroughs in the genome assembly and analysis of wild grape species have led to discoveries on grape evolution, from wild species' adaptation to environmental stress to grape domestication. We detail how diploid chromosome-scale genomes from wild Vitis spp. have enabled the identification of candidate disease-resistance and flower sex determination genes and the creation of the first Vitis graph-based pangenome. Finally, we explore how wild grape genomics can impact grape research and viticulture, including aspects such as data sharing, the development of functional genomics tools, and the acceleration of genetic improvement.

Chloroplast Genomes of Vitis flexuosa and Vitis amurensis: Molecular Structure, Phylogenetic, and Comparative Analyses for Wild Plant Conservation

The chloroplast genome plays a crucial role in elucidating genetic diversity and phylogenetic relationships. Vitis vinifera L. (grapevine) is an economically important species, prompting exploration of wild genetic resources to enhance stress resilience. We meticulously assembled the chloroplast genomes of two Korean Vitis L. species, V. flexuosa Thunb. and V. amurensis Rupr., contributing valuable data to the Korea Crop Wild Relatives inventory. Through exhaustive specimen collection spanning diverse ecological niches across South Korea, we ensured comprehensive representation of genetic diversity. Our analysis, which included rigorous codon usage bias assessment and repeat analysis, provides valuable insights into amino acid preferences and facilitates the identification of potential molecular markers. The assembled chloroplast genomes were subjected to meticulous annotation, revealing divergence hotspots enriched with nucleotide diversity, thereby presenting promising candidates for DNA barcodes. Additionally, phylogenetic analysis reaffirmed intra-genus relationships and identified related crops, shedding light on evolutionary patterns within the genus. Comparative examination with chloroplast genomes of other crops uncovered conserved sequences and variable regions, offering critical insights into genetic evolution and adaptation. Our study advances the understanding of chloroplast genomes, genetic diversity, and phylogenetic relationships within Vitis species, thereby laying a foundation for enhancing grapevine genetic diversity and resilience to environmental challenges.

Morphological Characterization of Fossil Vitis L. Seeds from the Gelasian of Italy by Seed Image Analysis

The discovery of well-preserved fossil Vitis L. seeds from the Gelasian stage in Italy has provided a unique opportunity to investigate the systematics of fossilized Vitis species. Through seed image analyses and elliptical Fourier transforms of fossil Vitis seeds from the sites Buronzo-Gifflenga and Castelletto Cervo II, we pointed out a strong relationship to the group of extant Eurasian Vitis species. However, classification analyses highlighted challenges in accurately assigning the fossil grape seeds to specific modern species. Morphological comparisons with modern Vitis species revealed striking similarities between the fossil seeds and V. vinifera subsp. sylvestris, as well as several other wild species from Asia. This close morphological resemblance suggests the existence of a population of V. vinifera sensu lato in Northen Italy during the Gelasian. These findings contributed to our understanding of the evolution and the complex interplay between ancient and modern Vitis species.

A super-pangenome of the North American wild grape species

BACKGROUND

Capturing the genetic diversity of wild relatives is crucial for improving crops because wild species are valuable sources of agronomic traits that are essential to enhance the sustainability and adaptability of domesticated cultivars. Genetic diversity across a genus can be captured in super-pangenomes, which provide a framework for interpreting genomic variations.

RESULTS

Here we report the sequencing, assembly, and annotation of nine wild North American grape genomes, which are phased and scaffolded at chromosome scale. We generate a reference-unbiased super-pangenome using pairwise whole-genome alignment methods, revealing the extent of the genomic diversity among wild grape species from sequence to gene level. The pangenome graph captures genomic variation between haplotypes within a species and across the different species, and it accurately assesses the similarity of hybrids to their parents. The species selected to build the pangenome are a great representation of the genus, as illustrated by capturing known allelic variants in the sex-determining region and for Pierce's disease resistance loci. Using pangenome-wide association analysis, we demonstrate the utility of the super-pangenome by effectively mapping short reads from genus-wide samples and identifying loci associated with salt tolerance in natural populations of grapes.

CONCLUSIONS

This study highlights how a reference-unbiased super-pangenome can reveal the genetic basis of adaptive traits from wild relatives and accelerate crop breeding research.

Wild grapes of Armenia: unexplored source of genetic diversity and disease resistance

The present study is the first in-depth research evaluating the genetic diversity and potential resistance of Armenian wild grapes utilizing DNA-based markers to understand the genetic signature of this unexplored germplasm. In the proposed research, five geographical regions with known viticultural history were explored. A total of 148 unique wild genotypes were collected and included in the study with 48 wild individuals previously collected as seed. A total of 24 nSSR markers were utilized to establish a fingerprint database to infer information on the population genetic diversity and structure. Three nSSR markers linked to the Ren1 locus were analyzed to identify potential resistance against powdery mildew. According to molecular fingerprinting data, the Armenian V. sylvestris gene pool conserves a high genetic diversity, displaying 292 different alleles with 12.167 allele per loci. The clustering analyses and diversity parameters supported eight genetic groups with 5.6% admixed proportion. The study of genetic polymorphism at the Ren1 locus revealed that 28 wild genotypes carried three R-alleles and 34 wild genotypes carried two R-alleles associated with PM resistance among analyzed 107 wild individuals. This gene pool richness represents an immense reservoir of under-explored genetic diversity and breeding potential. Therefore, continued survey and research efforts are crucial for the conservation, sustainable management, and utilization of Armenian wild grape resources in the face of emerging challenges in viticulture.

Species relationships within the genus Vitis based on molecular and morphological data

The grape genus Vitis L. includes the domesticated V. vinifera, which is one of the most important fruit crop, and also close relatives recognized as valuable germplasm resources for improving cultivars. To resolve some standing problems in the species relationships within the Vitis genus we analyzed diversity in a set of 90 accessions comprising most of Vitis species and some putative hybrids. We discovered single nucleotide polymorphisms (SNPs) in SANGER sequences of twelve loci and genotyped accessions at a larger number of SNPs using a previously developed SNP array. Our phylogenic analyses consistently identified: three clades in North America, one in East Asia, and one in Europe corresponding to V. vinifera. Using heterozygosity measurement, haplotype reconstruction and chloroplast markers, we identified the hybrids existing within and between clades. The species relationships were better assessed after discarding these hybrids from analyses. We also studied the relationships between phylogeny and morphological traits and found that several traits significantly correlated with the phylogeny. The American clade that includes important species such as V. riparia and V. rupestris showed a major divergence with all other clades based on both DNA polymorphisms and morphological traits.

Long-read, chromosome-scale assembly of Vitis rotundifolia cv. Carlos and its unique resistance to Xylella fastidiosa subsp. fastidiosa

BACKGROUND

Muscadine grape (Vitis rotundifolia) is resistant to many of the pathogens that negatively impact the production of common grape (V. vinifera), including the bacterial pathogen Xylella fastidiosa subsp. fastidiosa (Xfsf), which causes Pierce's Disease (PD). Previous studies in common grape have indicated Xfsf delays host immune response with a complex O-chain antigen produced by the wzy gene. Muscadine cultivars range from tolerant to completely resistant to Xfsf, but the mechanism is unknown.

RESULTS

We assembled and annotated a new, long-read genome assembly for 'Carlos', a cultivar of muscadine that exhibits tolerance, to build upon the existing genetic resources available for muscadine. We used these resources to construct an initial pan-genome for three cultivars of muscadine and one cultivar of common grape. This pan-genome contains a total of 34,970 synteny-constrained entries containing genes of similar structure. Comparison of resistance gene content between the 'Carlos' and common grape genomes indicates an expansion of resistance (R) genes in 'Carlos.' We further identified genes involved in Xfsf response by transcriptome sequencing 'Carlos' plants inoculated with Xfsf. We observed 234 differentially expressed genes with functions related to lipid catabolism, oxidation-reduction signaling, and abscisic acid (ABA) signaling as well as seven R genes. Leveraging public data from previous experiments of common grape inoculated with Xfsf, we determined that most differentially expressed genes in the muscadine response were not found in common grape, and three of the R genes identified as differentially expressed in muscadine do not have an ortholog in the common grape genome.

CONCLUSIONS

Our results support the utility of a pan-genome approach to identify candidate genes for traits of interest, particularly disease resistance to Xfsf, within and between muscadine and common grape.

Phylogenomic analyses using a new 1013-gene Vitaceae bait-set support major groups of North American Vitis

A set of newly designed Vitaceae baits targeting 1013 genes was employed to explore phylogenetic relationships among North American Vitis. Eurasian Vitis taxa including Vitis vinifera were found to be nested within North American Vitis subgenus Vitis. North American Vitis subgenus Vitis can be placed into nine main groups: the Monticola group, the Occidentales group, the Californica group, the Vinifera group (introduced from Eurasia), the Mustangensis group, the Palmata group, the Aestivalis group, the Labrusca group, and the Cinerea group. Strong cytonuclear discordances were detected in North American Vitis, with many species non-monophyletic in the plastid phylogeny, while monophyletic in the nuclear phylogeny. The phylogenomic analyses support recognizing four distinct species in the Vitis cinerea complex in North America: V. cinerea, V. baileyana, V. berlandieri, and V. simpsonii. Such treatment will better serve the conservation of wild Vitis diversity in North America. Yet the evolutionary history of Vitis is highly complex, with the concordance analyses indicating conflicting signals across the phylogeny. Cytonuclear discordances and Analyses using the Species Networks applying Quartets (SNaQ) method support extensive hybridizations in North American Vitis. The results further indicate that plastid genomes alone are insufficient for resolving the evolutionary history of plant groups that have undergone rampant hybridization, like the case in North American Vitis. Nuclear gene data are essential for species delimitation, identification and reconstructing evolutionary relationships; therefore, they are imperative for plant phylogenomic studies.

The mature phyllosphere microbiome of grapevine is associated with resistance against Plasmopara viticola

Phyllosphere microbiota represents a substantial but hardly explored reservoir for disease resistance mechanisms. The goal of our study was to understand the link between grapevine cultivars susceptibility to Plasmopara viticola, one of the most devastating leaf pathogens in viticulture, and the phyllosphere microbiota. Therefore, we analyzed a 16S rRNA gene library for the dominant phyllosphere bacterial phyla Alphaproteobacteria of seven Vitis genotypes at different developmental stages, i.e., flowering and harvesting, via amplicon sequencing. Young leaves had significantly higher Alphaproteobacterial richness and diversity without significant host-specificity. In contrast, the microbial communities of mature leaves were structurally distinct in accordance with P. viticola resistance levels. This statistically significant link between mature bacterial phyllosphere communities and resistant phenotypes was corroborated by beta diversity metrics and network analysis. Beyond direct host-driven effects via the provision of microhabitats, we found evidence that plants recruit for specific bacterial taxa that were likely playing a fundamental role in mediating microbe-microbe interactions and structuring clusters within mature communities. Our results on grape-microbiota interaction provide insights for targeted biocontrol and breeding strategies.

Coastal Wild Grapevine Accession (Vitis vinifera L. ssp. sylvestris) Shows Distinct Late and Early Transcriptome Changes under Salt Stress in Comparison to Commercial Rootstock Richter 110

Increase in soil salinity, driven by climate change, is a widespread constrain for viticulture across several regions, including the Mediterranean basin. The implementation of salt-tolerant varieties is sought after to reduce the negative impact of salinity in grape production. An accession of wild grapevine (Vitis vinifera L. ssp. sylvestris), named AS1B, found on the coastline of Asturias (Spain), could be of interest toward the achievement of salt-tolerant varieties, as it demonstrated the ability to survive and grow under high levels of salinity. In the present study, AS1B is compared against widely cultivated commercial rootstock Richter 110, regarding their survival capabilities, and transcriptomic profiles analysis allowed us to identify the genes by employing RNA-seq and gene ontology analyses under increasing salinity and validate (via RT-qPCR) seven salinity-stress-induced genes. The results suggest contrasting transcriptomic responses between AS1B and Richter 110. AS1B is more responsive to a milder increase in salinity and builds up specific mechanisms of tolerance over a sustained salt stress, while Richter 110 maintains a constitutive expression until high and prolonged saline inputs, when it mainly shows responses to osmotic stress. The genetic basis of AS1B's strategy to confront salinity could be valuable in cultivar breeding programs, to expand the current range of salt-tolerant rootstocks, aiming to improve the adaptation of viticulture against climate change.

Tannin phenotyping of the Vitaceae reveals a phylogenetic linkage of epigallocatechin in berries and leaves

BACKGROUND AND AIMS

Condensed tannins, responsible for berry and wine astringency, may have been selected during grapevine domestication. This work examines the phylogenetic distribution of condensed tannins throughout the Vitaceae phylogenetic tree.

METHODS

Green berries and mature leaves of representative true-to-type members of the Vitaceae were collected before 'véraison', freeze-dried and pulverized, and condensed tannins were measured following depolymerization by nucleophilic addition of 2-mercaptoethanol to the C4 of the flavan-3-ol units in an organic acidic medium. Reaction products were separated and quantified by ultrahigh pressure liquid chromatography/diode array detection/mass spectrometry.

KEY RESULTS AND CONCLUSIONS

The original ability to incorporate epigallocatechin (EGC) into grapevine condensed tannins was lost independently in both the American and Eurasian/Asian branches of the Vitaceae, with exceptional cases of reversion to the ancestral EGC phenotype. This is particularly true in the genus Vitis, where we now find two radically distinct groups differing with respect to EGC content. While Vitis species from Asia are void of EGC, 50 % of the New World Vitis harbour EGC. Interestingly, the presence of EGC is tightly coupled with the degree of leaf margin serration. Noticeably, the rare Asian EGC-forming species are phylogenetically close to Vitis vinifera, the only remnant representative of Vitis in Eurasia. Both the wild ancestral V. vinifera subsp. sylvestris as well as the domesticated V. vinifera subsp. sativa can accumulate EGC and activate galloylation biosynthesis that compete for photoassimilates and reductive power.

Genetic Diversity of Wild and Cultivated Muscadine Grapes (Vitis rotundifolia Michx.)

The muscadine (Vitis rotundifolia syn. Muscadinia rotundifolia) is an American grape species native to the southeastern United States that has been cultivated for centuries. Muscadines are one of three grape species in subgenus Muscadinia with a chromosome number of 2n = 40 (V. rotundifolia, Vitis munsoniana, and Vitis popenoei), making them genetically distinct from the European wine and table grape (Vitis vinifera) and other species in subgenus Euvitis. Crop improvement efforts have been continuous since the late 19th century, yet the germplasm that served as the foundation for early muscadine breeding efforts was sourced from a relatively small portion of their native range, mostly in the coastal plains of North Carolina. This study used the rhAmpSeq Vitis core panel haplotype markers to genotype 194 Muscadinia accessions from five cultivated populations and 15 wild populations collected across their native range. Wild populations from the western half of the native range were generally less genetically differentiated than hypothesized, but were genetically distinct from the material used in both past and present breeding efforts. One population collected from coastal North Carolina grouped closely with V. munsoniana accessions despite being well outside the reported range for that species. Principal coordinate and structure analyses revealed three main groups within the 194 accessions: one for cultivated material, one for wild V. rotundifolia, and one for V. munsoniana and V. popenoei. At K = 5, structure results showed that more recent muscadine cultivars are further differentiated from wild accessions and varieties. These analyses confirmed our hypothesis that muscadine cultivars are genetically differentiated from their wild counterparts. This study also showed that genetic diversity in V. rotundifolia is not equally distributed across its native range and that the limited number of genotypes used in crop improvement efforts has not fully utilized the genetic diversity within the species.

Recombination patterns in coronaviruses

As shown during the SARS-CoV-2 pandemic, phylogenetic and phylodynamic methods are essential tools to study the spread and evolution of pathogens. One of the central assumptions of these methods is that the shared history of pathogens isolated from different hosts can be described by a branching phylogenetic tree. Recombination breaks this assumption. This makes it problematic to apply phylogenetic methods to study recombining pathogens, including, for example, coronaviruses. Here, we introduce a Markov chain Monte Carlo approach that allows inference of recombination networks from genetic sequence data under a template switching model of recombination. Using this method, we first show that recombination is extremely common in the evolutionary history of SARS-like coronaviruses. We then show how recombination rates across the genome of the human seasonal coronaviruses 229E, OC43 and NL63 vary with rates of adaptation. This suggests that recombination could be beneficial to fitness of human seasonal coronaviruses. Additionally, this work sets the stage for Bayesian phylogenetic tracking of the spread and evolution of SARS-CoV-2 in the future, even as recombinant viruses become prevalent.

The Role of Biostimulants as Alleviators of Biotic and Abiotic Stresses in Grapevine: A Review

The viticulture and wine industry contribute to the economy and reputation of many countries all over the world. With the predicted climate change, a negative impact on grapevine physiology, growth, production, and quality of berries is expected. On the other hand, the impact of these changes in phytopathogenic fungi development, survival rates, and host susceptibility is unpredictable. Grapevine fungal diseases control has been a great challenge to winegrowers worldwide. The use of chemicals in viticulture is high, which can result in the development of pathogen resistance, increasingly raising concerns regarding residues in wine and effects on human and environmental health. Promoting sustainable patterns of production is one of the overarching objectives and essential requirements for sustainable development. Alternative holistic approaches, such as those making use of biostimulants, are emerging in order to reduce the consequences of biotic and abiotic stresses in the grapevine, namely preventing grape fungal diseases, improving grapevine resistance to water stress, and increasing yield and berry quality.

Extent of wild-to-crop interspecific introgression in grapevine (Vitis vinifera) as a consequence of resistance breeding and implications for the crop species definition

Over the past two centuries, introgression through repeated backcrossing has introduced disease resistance from wild grape species into the domesticated lineage Vitis vinifera subsp. sativa. Introgression lines are being cultivated over increasing vineyard surface areas, as their wines now rival in quality those obtained from preexisting varieties. There is, however, a lot of debate about whether and how wine laws defining commercial product categories, which are based on the classification of V. vinifera and interspecific hybrid grapes, should be revised to accommodate novel varieties that do not fit either category. Here, we developed a method of multilocus genotype analysis using short-read resequencing to identify haplotypic blocks of wild ancestry in introgression lines and quantify the physical length of chromosome segments free-of-introgression or with monoallelic and biallelic introgression. We used this genomic data to characterize species, hybrids and introgression lines and show that newly released resistant varieties contain 76.5-94.8% of V. vinifera DNA. We found that varietal wine ratings are not always commensurate with the percentage of V. vinifera ancestry and linkage drag of wild alleles around known resistance genes persists over at least 7.1-11.5 Mb, slowing down the recovery of the recurrent parental genome. This method also allowed us to identify the donor species of known resistance haplotypes, define the ancestry of wild genetic background in introgression lines with complex pedigrees, validate the ancestry of the historic varieties Concord and Norton, and unravel sample curation errors in public databases.

VaAPRT3 Gene is Associated With Sex Determination in Vitis amurensis

In the past decade, progress has been made in sex determination mechanism in Vitis. However, genes responsible for sexual differentiation and its mechanism in V. amurensis remain unknown. Here, we identify a sex determination candidate gene coding adenine phosphoribosyl transferase 3 (VaAPRT3) in V. amurensis. Cloning and sequencing of the VaAPRT3 gene allowed us to develop a molecular marker able to discriminate female individuals from males or hermaphrodites based on a 22-bp InDel. Gene expression and endogenous cytokinin content analysis revealed that the VaAPRT3 gene is involved in sex determination or, to be precise, in female organ differentiation, through regulating cytokinin metabolism in V. amurensis. This study enlarged the understanding of sex determination mechanism in the genus Vitis, and the sex marker could be used as a helpful tool for sexual identification in breeding programs as well as in investigation and collection of V. amurensis germplasms.

Vitisshizishanensis, a new species of the grape genus from Hubei province, China

Vitisshizishanensis (Vitaceae), a new species from Hubei, China, is described and illustrated. It is morphologically similar to V.flexuosa and V.bryoniifolia, but differs in leaf lobing and pubescence. It can be easily distinguished from the two species based on its glabrous or with very sparse arachnoid tomentum on the abaxial mature leaf surface, and its unlobed to 3-7 lobed leaves. A detailed description, along with photographs for the new species, and a table for morphological comparisons with similar Vitis species, are also provided.

Grape Transcriptome Response to Powdery Mildew Infection: Comparative Transcriptome Profiling of Chinese Wild Grapes Provides Insights Into Powdery Mildew Resistance

Erysiphe necator, the fungal pathogen of grape powdery mildew disease, poses a great threat to the grape market and the wine industry. To better understand the molecular basis of grape responses to E. necator, we performed comparative transcriptome profiling on two Chinese wild grape accessions with varying degrees of resistance to E. necator. At 6-, 24-, and 96-h postinoculation of E. necator, 2,856, 2,678, and 1,542 differentially expressed genes (DEGs) were identified in the susceptible accession Vitis pseudoreticulata 'Hunan-1', and at those same time points, 1,921, 2,498, and 3,249 DEGs, respectively, were identified in the resistant accession V. quinquangularis 'Shang-24'. 'Hunan-1' had a substantially larger fraction of down-regulated genes than 'Shang-24' at every infection stage. Analysis of DEGs revealed that up-regulated genes were mostly associated with defense response and disease resistance-related metabolite biosynthesis, and such signaling genes were significantly suppressed in 'Hunan-1'. Interestingly, fatty acid biosynthesis- and elongation-related genes were suppressed by the fungus in the 'Shang-24' accession but somehow induced in the 'Hunan-1' accession, consistent with the concept that E. necator is likely to be a fatty acid auxotroph that requires lipids from the host. Moreover, genes involved in biosynthesis and signaling of phytohormones, such as jasmonic acid and cytokinin, as well as genes encoding protein kinases and nucleotide-binding domain leucine-rich repeat proteins, differentially responded to E. necator in the two wild grapes. The variation of gene regulation associated with nutrient uptake by the fungus and with signaling transduction and pathogen recognition suggests a multilayered regulatory network that works in concert to assist in the establishment of fungal pathogen infections.

Introgression among North American wild grapes (Vitis) fuels biotic and abiotic adaptation

BACKGROUND

Introgressive hybridization can reassort genetic variants into beneficial combinations, permitting adaptation to new ecological niches. To evaluate evolutionary patterns and dynamics that contribute to introgression, we investigate six wild Vitis species that are native to the Southwestern United States and useful for breeding grapevine (V. vinifera) rootstocks.

RESULTS

By creating a reference genome assembly from one wild species, V. arizonica, and by resequencing 130 accessions, we focus on identifying putatively introgressed regions (pIRs) between species. We find six species pairs with signals of introgression between them, comprising up to ~ 8% of the extant genome for some pairs. The pIRs tend to be gene poor, located in regions of high recombination and enriched for genes implicated in disease resistance functions. To assess potential pIR function, we explore SNP associations to bioclimatic variables and to bacterial levels after infection with the causative agent of Pierce's disease (Xylella fastidiosa). pIRs are enriched for SNPs associated with both climate and bacterial levels, suggesting that introgression is driven by adaptation to biotic and abiotic stressors.

CONCLUSIONS

Altogether, this study yields insights into the genomic extent of introgression, potential pressures that shape adaptive introgression, and the evolutionary history of economically important wild relatives of a critical crop.

Vitis Species from the Southwestern United States Vary in Their Susceptibility to Powdery Mildew

The European grapevine (Vitis vinifera L.) has been cultivated in North America for about 500 years. One of the major limitations to its culture is the powdery mildew (PM) fungus, Erysiphe necator Schw. This study reports on the most extensive screening of Vitis species from the southwestern United States and northern Mexico for resistance to PM, testing 147 accessions of 13 Vitis species. In addition, Vitis vinifera cv. Carignane, a highly susceptible wine grape cultivar, was used as a reference to evaluate the effect of the inoculum 14 days postinoculation. Inoculation was done with a vacuum-operated settling tower using a broadly virulent isolate of E. necator, the C-strain. Resistant accessions (nine), moderately susceptible accessions (39), and highly susceptible accessions (99) were detected. The resistant accessions were then inoculated with an additional fungal isolate, e1-101, and they retained their resistance. Vitis species susceptibility was not associated with a North-South gradation, but Western species were more susceptible than Midwestern and Eastern species. All five of the V. monticola accessions were susceptible, as were the accessions of V. treleasei. The species V. acerifolia, V. candicans, V. cinerea, and V. × doaniana had significantly more resistant to moderately susceptible accessions compared with V. arizonica, V. berlandieri, V. californica, V. × champinii, V. girdiana, V. riparia, and V. rupestris, which had relatively more susceptible accessions than the other species. This research identified new sources of PM resistance in Vitis from the southwestern United States that could be incorporated into PM resistance breeding programs throughout the world.

Assessment of Chemopreventive Potential of the Plant Extracts against Liver Cancer Using HepG2 Cell Line

The edible parts of the plants Camellia sinensis, Vitis vinifera and Withania somnifera were extensively used in ancient practices such as Ayurveda, owing to their potent biomedical significance. They are very rich in secondary metabolites such as polyphenols, which are very good antioxidants and exhibit anti-carcinogenic properties. This study aims to evaluate the anti-cancerous properties of these plant crude extracts on human liver cancer HepG2 cells. The leaves of Camellia sinensis, Withania somnifera and the seeds of Vitis vinifera were collected and methanolic extracts were prepared. Then, these extracts were subjected to DPPH, α- amylase assays to determine the antioxidant properties. A MTT assay was performed to investigate the viability of the extracts of HepG2 cells, and the mode of cell death was detected by Ao/EtBr staining and flow cytometry with PI Annexin- V FITC dual staining. Then, the protein expression of BAX and BCl2 was studied using fluorescent dye to determine the regulation of the BAX and BCl2 genes. We observed that all the three extracts showed the presence of bioactive compounds such as polyphenols or phytochemicals. The W. somnifera bioactive compounds were found to have the highest anti-proliferative activity on human liver cancer cells.

Diploid chromosome-scale assembly of the Muscadinia rotundifolia genome supports chromosome fusion and disease resistance gene expansion during Vitis and Muscadinia divergence

Muscadinia rotundifolia, the muscadine grape, has been cultivated for centuries in the southeastern United States. M. rotundifolia is resistant to many of the pathogens that detrimentally affect Vitis vinifera, the grape species commonly used for winemaking. For this reason, M. rotundifolia is a valuable genetic resource for breeding. Single-molecule real-time reads were combined with optical maps to reconstruct the two haplotypes of each of the 20 M. rotundifolia cv. Trayshed chromosomes. The completeness and accuracy of the assembly were confirmed using a high-density linkage map. Protein-coding genes were annotated using an integrated and comprehensive approach. This included using full-length cDNA sequencing (Iso-Seq) to improve gene structure and hypothetical spliced variant predictions. Our data strongly support that Muscadinia chromosomes 7 and 20 are fused in Vitis and pinpoint the location of the fusion in Cabernet Sauvignon and PN40024 chromosome 7. Disease-related gene numbers in Trayshed and Cabernet Sauvignon were similar, but their clustering locations were different. A dramatic expansion of the Toll/Interleukin-1 Receptor-like Nucleotide-Binding Site Leucine-Rich Repeat (TIR-NBS-LRR) class was detected on Trayshed chromosome 12 at the Resistance to Uncinula necator 1 (RUN1)/Resistance to Plasmopara viticola 1 (RPV1) locus, which confers strong dominant resistance to powdery and downy mildews. A genome browser, annotation, and Blast tool for Trayshed are available at www.grapegenomics.com.

High-Throughput Sequencing Indicates Novel Varicosavirus, Emaravirus, and Deltapartitivirus Infections in Vitis coignetiae

Vitis coignetiae samples were collected from several locations in the northern area of Japan, and virome analysis using a high-throughput sequencing technique was performed. The data indicated that some of the collected samples were in mixed infections by various RNA viruses. Among these viruses, three were identified as newly recognized species with support of sequence identity and phylogenetic analysis. The viruses have been provisionally named the Vitis varicosavirus, Vitis emaravirus, and Vitis crypticvirus, and were assigned to the genus Varicosavirus, Emaravirus, and Deltapartitivirus, respectively.

Back to the Origins: Background and Perspectives of Grapevine Domestication

Domestication is a process of selection driven by humans, transforming wild progenitors into domesticated crops. The grapevine (Vitis vinifera L.), besides being one of the most extensively cultivated fruit trees in the world, is also a fascinating subject for evolutionary studies. The domestication process started in the Near East and the varieties obtained were successively spread and cultivated in different areas. Whether the domestication occurred only once, or whether successive domestication events occurred independently, is a highly debated mystery. Moreover, introgression events, breeding and intense trade in the Mediterranean basin have followed, in the last thousands of years, obfuscating the genetic relationships. Although a succession of studies has been carried out to explore grapevine origin and different evolution models are proposed, an overview of the topic remains pending. We review here the findings obtained in the main phylogenetic and genomic studies proposed in the last two decades, to clarify the fundamental questions regarding where, when and how many times grapevine domestication took place. Finally, we argue that the realization of the pan-genome of grapes could be a useful resource to discover and track the changes which have occurred in the genomes and to improve our understanding about the domestication.

Multiple independent recombinations led to hermaphroditism in grapevine

We studied the grape sex-determining region (SDR) in 12 Vitis genomes and demonstrated its conservation across 556 genotypes including 193 accessions from 47 world-wide wild grapevine species and 363 accessions of cultivated grapevine. Although the grape SDR is recombination free in all wild species, we found two distinct hermaphrodite (H) haplotypes (H1 and H2) among the cultivated grapevines, both chimeras of male (M) and female (f) haplotypes. The two independent recombinations carry different genetic signatures which long predate the domestication of grapevine, suggesting independent evolutions of this trait in wild European grapevine gene pools prior to human domestication.

Hermaphroditic (perfect) flowers were a key trait in grapevine domestication, enabling a drastic increase in yields due to the efficiency of self-pollination in the domesticated grapevine (Vitis vinifera L. ssp. vinifera). In contrast, all extant wild Vitis species are dioecious, each plant having only male or female flowers. In this study, we identified the male (M) and female (f) haplotypes of the sex-determining region (SDR) in the wild grapevine species V. cinerea and confirmed the boundaries of the SDR. We also demonstrated that the SDR and its boundaries are precisely conserved across the Vitis genus using shotgun resequencing data of 556 wild and domesticated accessions from North America, East Asia, and Europe. A high linkage disequilibrium was found at the SDR in all wild grape species, while different recombination signatures were observed along the hermaphrodite (H) haplotype of 363 cultivated accessions, revealing two distinct H haplotypes, named H1 and H2. To further examine the H2 haplotype, we sequenced the genome of two grapevine cultivars, 'Riesling' and 'Chardonnay'. By reconstructing the first two H2 haplotypes, we estimated the divergence time between H1 and H2 haplotypes at ∼6 million years ago, which predates the domestication of grapevine (∼8,000 y ago). Our findings emphasize the important role of recombination suppression in maintaining dioecy in wild grape species and lend additional support to the hypothesis that at least two independent recombination events led to the reversion to hermaphroditism in grapevine.

Genetic diversity and population structure in Vitis species illustrate phylogeographic patterns in eastern North America

Geographical distribution and diversity of current plant species have been strongly shaped by climatic oscillations during the Quaternary. Analysing the resulting divergence among species and differentiation within species is crucial to understand the evolution of taxa like the Vitis genus, which provides very useful genetic resources for grapevine improvement and might reveal original recolonization patterns due to growth habit and dispersal mode. Here, we studied the genetic structure in natural populations of three species from eastern North America: Vitis aestivalis, V. cinerea and V. riparia using different marker types. Vitis aestivalis and V. cinerea showed higher diversity than V. riparia. The two former species are less differentiated, confirming an earlier divergence of V. riparia. V. aestivalis and V. riparia exhibited different genetic groups on both sides of the Appalachian Mountains that could mirror different recolonization routes from southern refugia. Genetic structure was stronger in V. cinerea, for which two varieties (var. berlandieri and var. cinerea) are morphologically recognized. Our results confirm this distinction and suggest the existence of three other lineages within var. cinerea. These discontinuities appear linked to adaptation of var. berlandieri to dry and limy areas of Texas and partially to the Mississippi River Valley. Rapid range expansions from refugia upon climate warming are also suggested by the low linkage disequilibrium values observed. Furthermore, large variation for downy mildew resistance was observed in the three species. Our findings appeared consistent with the vegetation history of eastern North America.

Population structure of Erysiphe necator on domesticated and wild vines in the Middle East raises questions on the origin of the grapevine powdery mildew pathogen

Plant pathogens usually originate and diversify in geographical regions where hosts and pathogens co-evolve. Erysiphe necator, the causal agent of grape powdery mildew, is a destructive pathogen of grapevines worldwide. Although Eastern US is considered the centre of origin and diversity of E. necator, previous reports on resistant native wild and domesticated Asian grapevines suggest Asia as another possible origin of the pathogen. By using multi-locus sequencing, microsatellites and a novel application of amplicon sequencing (AmpSeq), we show that the population of E. necator in Israel is composed of three genetic groups: Groups A and B that are common worldwide, and a new group IL, which is genetically differentiated from any known group in Europe and Eastern US. Group IL showed distinguished ecological characteristics: it was dominant on wild and traditional vines (95%); its abundance increased along the season; and was more aggressive than A and B isolates on both wild and domesticated vines. The low genetic diversity within group IL suggests that it has invaded Israel from another origin. Therefore, we suggest that the Israeli E. necator population was founded by at least two invasions, of which one could be from a non-East American source, possibly from Asian origin.

Genetic analysis reveals an east-west divide within North American Vitis species that mirrors their resistance to Pierce's disease

Pierce’s disease (PD) caused by the bacterium Xylella fastidiosa is a deadly disease of grapevines. This study used 20 SSR markers to genotype 326 accessions of grape species collected from the southeastern and southwestern United States, Mexico and Costa Rica. Two hundred sixty-six of these accessions, and an additional 12 PD resistant hybrid cultivars developed from southeastern US grape species, were evaluated for PD resistance. Disease resistance was evaluated by quantifying the level of bacteria in stems and measuring PD symptoms on the canes and leaves. Both Bayesian clustering and principal coordinate analyses identified two groups with an east-west divide: group 1 consisted of grape species from the southeastern US and Mexico, and group 2 consisted of accessions collected from the southwestern US and Mexico. The Sierra Madre Oriental mountain range appeared to be a phylogeographic barrier. The state of Texas was identified as a potential hybridization zone. The hierarchal STRUCTURE analysis on each group showed clustering of unique grape species. An east-west divide was also observed for PD resistance. With the exception of Vitis candicans and V. cinerea accessions collected from Mexico, all other grape species as well as the resistant southeastern hybrid cultivars were susceptible to the disease. Southwestern US grape accessions from drier desert regions showed stronger resistance to the disease. Strong PD resistance was observed within three distinct genetic clusters of V. arizonica which is adapted to drier environments and hybridizes freely with other species across its wide range.

The wild grape genome sequence provides insights into the transition from dioecy to hermaphroditism during grape domestication

Background

A key step in domestication of the grapevine was the transition from separate sexes (dioecy) in wild Vitis vinifera ssp. sylvestris (V. sylvestris) to hermaphroditism in cultivated Vitis vinifera ssp. sativa (V. vinifera). It is known that V. sylvestris has an XY system and V. vinifera a modified Y haplotype (Yh) and that the sex locus is small, but it has not previously been precisely characterized.

Results

We generate a high-quality de novo reference genome for V. sylvestris, onto which we map whole-genome re-sequencing data of a cross to locate the sex locus. Assembly of the full X, Y, and Yh haplotypes of V. sylvestris and V. vinifera sex locus and examining their gene content and expression profiles during flower development in wild and cultivated accessions show that truncation and deletion of tapetum and pollen development genes on the X haplotype likely causes male sterility, while the upregulation of a Y allele of a cytokinin regulator (APRT3) may cause female sterility. The downregulation of this cytokinin regulator in the Yh haplotype may be sufficient to trigger reversal to hermaphroditism. Molecular dating of X and Y haplotypes is consistent with the sex locus being as old as the Vitis genus, but the mechanism by which recombination was suppressed remains undetermined.

Conclusions

We describe the genomic and evolutionary characterization of the sex locus of cultivated and wild grapevine, providing a coherent model of sex determination in the latter and for transition from dioecy to hermaphroditism during domestication.

Genetic mapping and survey of powdery mildew resistance in the wild Central Asian ancestor of cultivated grapevines in Central Asia

Cultivated grapevines (Vitis vinifera) lack resistance to powdery mildew (PM) with few exceptions. Resistance to this pathogen within V. vinifera has been reported in earlier studies and identified as the Ren1 locus in two Central Asian table grape accessions. Other PM-resistant cultivated varieties and accessions of the wild ancestor V. vinifera subsp. sylvestris were soon identified raising questions regarding the origin of the resistance. In this study, F1 breeding populations were developed with a PM susceptible V. vinifera subsp. vinifera breeding line and a PM-resistant subsp. sylvestris accession. Genotyping was carried out with five Ren1 locus linked SSR markers. A PM resistance locus explaining up to 96% of the phenotypic variation was identified in the same genomic position, where the Ren1 locus was previously reported. New SSR marker alleles linked with the resistance locus were identified. We report results of PM resistance in multiple accessions of subsp. sylvestris collected as seed lots or cuttings from five countries in the Caucasus and Central Asia. A total of 20 females from 11 seed lots and 19 males from nine seed lots collected from Georgia, Armenia, and Azerbaijan were resistant to PM. Three male and one female plant collected as cuttings from Afghanistan and Iran were also resistant to PM. Allelic analysis of markers linked with the Ren1 locus in conjunction with disease evaluation data found a high diversity of allelic haplotypes, which are only possible via recombination events occurring over a long time period. Sequence analysis of two alleles of the SSR marker that cosegregates with the resistance found SNPs that were present in the wild progenitor and in cultivated forms. Variable levels of PM resistance among the tested accessions were also observed. These lines of evidence suggest that the powdery mildew fungus may have been present in Asia for a longer time than currently thought, giving the wild progenitor V. vinifera subsp. sylvestris time to coevolve with and develop resistance to this pathogen.

Ecology and Genetics of Natural Populations of North American Vitis Species Used as Rootstocks in European Grapevine Breeding Programs

Three North American Vitis species (V. riparia, V. berlandieri, V. rupestris) became widely used in rootstock breeding programs following the expansion of North American pests and diseases introduced in vineyards of the world during the 19th century. When they escape, they become feral in the most dynamic parts of Mediterranean floodplains. To better understand this ongoing process, we studied the ecology of Vitis species in their native sympatric range. We analyzed in deep 61 plots of 710 m2 containing Vitaceae species along 216 km of the Buffalo River and adjacent plateaus (Arkansas, United States). We investigated the populations structure and genetics of the Vitis complex (i.e., possible hybrids and the Vitis species) and the sharing of habitats with other Vitaceae (Muscadinia rotundifolia and Parthenocissus quinquefolia). Vitaceae share space according to their life strategies and microhabitat along ecological gradients. The plateau niche seems optimal for V. berlandieri and V. aestivalis. V. berlandieri is also found in alluvial zones. The most erosive parts of the river are colonized by V. rupestris, whereas the first terraces include most of the M. rotundifolia populations. Vitis riparia and Parthenocissus live in the largest range of forest habitats, from plateaus to alluvial forests, and from the forest floor to the canopy, with the highest densities along the river. Interestingly, natural hybridization can occur, but establishment success is rare and limited to alluvial forests. In their native range, these populations are controlled by biotic and abiotic conditions. In Europe, the biotic relations among species are different. Our study shows that V. riparia and its hybrids could be the best candidates for a large scale invasion.

The genetic basis of sex determination in grapes

It remains a major challenge to identify the genes and mutations that lead to plant sexual differentiation. Here, we study the structure and evolution of the sex-determining region (SDR) in Vitis species. We report an improved, chromosome-scale Cabernet Sauvignon genome sequence and the phased assembly of nine wild and cultivated grape genomes. By resolving twenty Vitis SDR haplotypes, we compare male, female, and hermaphrodite haplotype structures and identify sex-linked regions. Coupled with gene expression data, we identify a candidate male-sterility mutation in the VviINP1 gene and potential female-sterility function associated with the transcription factor VviYABBY3. Our data suggest that dioecy has been lost during domestication through a rare recombination event between male and female haplotypes. This work significantly advances the understanding of the genetic basis of sex determination in Vitis and provides the information necessary to rapidly identify sex types in grape breeding programs.

Grapevine is one of a few ancestrally dioecious crops that are reverted to hermaphroditism during domestication. Here, the authors identify candidate genes related to male- and female-sterility in grapes and describe the genetic process that led to hermaphroditism during domestication.

Draft genome of the Native American cold hardy grapevine Vitis riparia Michx. 'Manitoba 37'

Vitis riparia, a critically important Native American grapevine species, is used globally in rootstock and scion breeding and contributed to the recovery of the French wine industry during the mid-19th century phylloxera epidemic. This species has abiotic and biotic stress tolerance and the largest natural geographic distribution of the North American grapevine species. Here we report an Illumina short-read 369X coverage, draft de novo heterozygous genome sequence of V. riparia Michx. 'Manitoba 37' with the size of ~495 Mb for 69,616 scaffolds and a N50 length of 518,740 bp. Using RNAseq data, 40,019 coding sequences were predicted and annotated. Benchmarking with Universal Single-Copy Orthologs (BUSCO) analysis of predicted gene models found 96% of the complete BUSCOs in this assembly. The assembly continuity and completeness were further validated using V. riparia ESTs, BACs, and three de novo transcriptome assemblies of three different V. riparia genotypes resulting in >98% of respective sequences/transcripts mapping with this assembly. Alignment of the V. riparia assembly and predicted CDS with the latest V. vinifera 'PN40024' CDS and genome assembly showed 99% CDS alignment and a high degree of synteny. An analysis of plant transcription factors indicates a high degree of homology with the V. vinifera transcription factors. QTL mapping to V. riparia 'Manitoba 37' and V. vinifera PN40024 has identified genetic relationships to phenotypic variation between species. This assembly provides reference sequences, gene models for marker development and understanding V. riparia's genetic contributions in grape breeding and research.

Nuclear and Chloroplast Sequences Resolve the Enigmatic Origin of the Concord Grape

Despite the commercial importance of the Concord grape, its origin has remained unresolved for over 150 years without a comprehensive phylogenetic analysis. In this study we aimed to reconstruct the evolutionary history of the Concord grape using sequence data from four nuclear markers (AT103, GAI1, PHYA, and SQD1), six plastid markers (matK, psbA-trnH, petN-trnC, ycf1, trnL-F, and trnS-G), and the plastid genome. We sampled extensively the Vitis species native to northeastern North America as well as representative species from Europe and Asia, including the commercially important Vitis vinifera (wine grape), a native European species with hermaphroditic flowers, and its wild progenitor, V. vinifera subsp. sylvestris. We also sequenced the plastid genome of one accession of the Concord grape and compared the plastid genome data to the recently published data set of Vitis plastomes. Phylogenetic analyses of the plastid and nuclear data using maximum likelihood and Bayesian inference support the hybrid origin of the Concord grape. The results clearly pinpoint the wine grape, V. vinifera, as the maternal donor and the fox grape, Vitis labrusca, which is common in northeastern North America, as the paternal donor. Moreover, we infer that the breeding history of the Concord grape must have involved the backcrossing of the F1 hybrid with the paternal parent V. labrusca. This backcrossing also explains the higher morphological similarity of the Concord grape to V. labrusca than to V. vinifera. This study provides concrete genetic evidence for the hybrid origin of a widespread Vitis cultivar and is, therefore, promising for similar future studies focused on resolving ambiguous origins of major crops or to create successful hybrid fruit crops.

Genetic Diversity and Population Structure in a Vitis spp. Core Collection Investigated by SNP Markers

Single nucleotide polymorphism (SNP) genotyping arrays are powerful tools to measure the level of genetic polymorphism within a population. The coming of next-generation sequencing technologies led to identifying thousands and millions of SNP loci useful in assessing the genetic diversity. The Vitis genotyping array, containing 18k SNP loci, has been developed and used to detect genetic diversity of Vitis vinifera germplasm. So far, this array was not validated on non-vinifera genotypes used as grapevine rootstocks. In this work, a core collection of 70 grapevine rootstocks, composed of individuals belonging to Vitis species not commonly used in the breeding programs, was genotyped using the 18k SNP genotyping array. SNP results were compared to the established SSR (Simple Sequence Repeat) markers in terms of heterozygosity and genetic structure of the core collection. Genotyping array has proved to be a valuable tool for genotyping of grapevine rootstocks, with more than 90% of SNPs successfully amplified. Structure analysis detected a high degree of admixed genotypes, supported by the complex genetic background of non-vinifera germplasm. Moreover, SNPs clearly differentiated non-vinifera and vinifera germplasm. These results represent a first step in studying the genetic diversity of non-conventional breeding material that will be used to select rootstocks with high tolerance to limiting environmental conditions.

Untangling the Evolution of American Wild Grapes: Admixed Species and How to Find Them

Natural hybridization and introgression are central evolutionary processes in grape genus (Vitis). On the other hand, the interspecific relationships among grapes, the directionality of the inferred admixture events and the parents of hybrids are not yet completely clarified. The grapes are economically important crops characterized by tendrils used to climb on the trees and the fruits harvested by humans especially for the consumption or to produce wines and liquors. The American grapes (ca. 30 species) are recognized as an important resource because they show biotic and abiotic resistances. We analyzed 3,885 genome-wide SNPs from 31 American Vitis species using the TreeMix software combined with the f3 and f4 tests. This approach allowed us to infer phylogenetic relationships and to explore the natural admixture among taxa. Our results confirmed the existence of all hybrid species recognized in literature (V. x champinii, V. x doaniana, V. x novae-angliae, and V. x slavinii), identifying their most likely parent species and provided evidence of additional gene flows between distantly related species. We discuss our results to elucidate the origin of American wild grapes, demonstrating that admixture events have ancient origins. We observe that gene flows have involved taxa currently spread through the southern regions of North America. Consequently, we propose that glacial cycles could have triggered the contact between interfertile taxa promoting local hybridization events. We conclude by discussing the phylogenetic implications of our findings and showing that TreeMix can provide novel insights into the evolutionary history of grapes.

Gene duplication and transposition of mobile elements drive evolution of the Rpv3 resistance locus in grapevine

A wild grape haplotype (Rpv3-1) confers resistance to Plasmopara viticola. We mapped the causal factor for resistance to an interval containing a TIR-NB-LRR (TNL) gene pair that originated 1.6-2.6 million years ago by a tandem segmental duplication. Transient coexpression of the TNL pair in Vitis vinifera leaves activated pathogen-induced necrosis and reduced sporulation compared with control leaves. Even though transcripts of the TNL pair from the wild haplotype appear to be partially subject to nonsense-mediated mRNA decay, mature mRNA levels in a homozygous resistant genotype were individually higher than the mRNA trace levels observed for the orthologous single-copy TNL in sensitive genotypes. Allelic expression imbalance in a resistant heterozygote confirmed that cis-acting regulatory variation promotes expression in the wild haplotype. The movement of transposable elements had a major impact on the generation of haplotype diversity, altering the DNA context around similar TNL coding sequences and the GC-content in their proximal 5'-intergenic regions. The wild and domesticated haplotypes also diverged in conserved single-copy intergenic DNA, but the highest divergence was observed in intraspecific and not in interspecific comparisons. In this case, introgression breeding did not transgress the genetic boundaries of the domesticated species, because haplotypes present in modern varieties sometimes predate speciation events between wild and cultivated species.

Construction of a High-Density Genetic Map and Mapping of Firmness in Grapes (Vitis vinifera L.) Based on Whole-Genome Resequencing

Berry firmness is one of the most important quality traits in table grapes. The underlying molecular and genetic mechanisms for berry firmness remain unclear. We constructed a high-density genetic map based on whole-genome resequencing to identify loci associated with berry firmness. The genetic map had 19 linkage groups, including 1662 bin markers (26,039 SNPs), covering 1463.38 cM, and the average inter-marker distance was 0.88 cM. An analysis of berry firmness in the F1 population and both parents for three consecutive years revealed continuous variability in F1, with a distribution close to the normal distribution. Based on the genetic map and phenotypic data, three potentially significant quantitative trait loci (QTLs) related to berry firmness were identified by composite interval mapping. The contribution rate of each QTL ranged from 21.5% to 28.6%. We identified four candidate genes associated with grape firmness, which are related to endoglucanase, abscisic acid (ABA), and transcription factors. A qRT-PCR analysis revealed that the expression of abscisic-aldehyde oxidase-like gene (VIT_18s0041g02410) and endoglucanase 3 gene (VIT_18s0089g00210) in Muscat Hamburg was higher than in Crimson Seedless at the veraison stage, which was consistent with that of parent berry firmness. These results confirmed that VIT_18s0041g02410 and VIT_18s0089g00210 are candidate genes associated with berry firmness.

Haplotyping the Vitis collinear core genome with rhAmpSeq improves marker transferability in a diverse genus

Transferable DNA markers are essential for breeding and genetics. Grapevine (Vitis) breeders utilize disease resistance alleles from congeneric species ~20 million years divergent, but existing Vitis marker platforms have cross-species transfer rates as low as 2%. Here, we apply a marker strategy targeting the inferred Vitis core genome. Incorporating seven linked-read de novo assemblies and three existing assemblies, the Vitis collinear core genome is estimated to converge at 39.8 Mb (8.67% of the genome). Adding shotgun genome sequences from 40 accessions enables identification of conserved core PCR primer binding sites flanking polymorphic haplotypes with high information content. From these target regions, we develop 2,000 rhAmpSeq markers as a PCR multiplex and validate the panel in four biparental populations spanning the diversity of the Vitis genus, showing transferability increases to 91.9%. This marker development strategy should be widely applicable for genetic studies in many taxa, particularly those ~20 million years divergent.

X-ray phase contrast imaging of Vitis spp. buds shows freezing pattern and correlation between volume and cold hardiness

Grapevine (Vitis spp.) buds must survive winter temperatures in order to resume growth when suitable conditions return in spring. They do so by developing cold hardiness through deep supercooling, but the mechanistic process of supercooling in buds remains largely unknown. Here we use synchrotron X-ray phase contrast imaging to study cold hardiness-related characteristics of V. amurensis, V. riparia, and V. vinifera buds: time-resolved 2D imaging was used to visualize freezing; and microtomography was used to evaluate morphological changes during deacclimation. Bud cold hardiness was determined (low temperature exotherms; LTEs) using needle thermocouples during 2D imaging as buds were cooled with a N₂ gas cryostream. Resolution in 2D imaging did not allow for ice crystal identification, but freezing was assessed by movement of tissues coinciding with LTE values. Freezing was observed to propagate from the center of the bud toward the outer bud scales. The freezing events observed lasted several minutes. Additionally, loss of supercooling ability appears to be correlated with increases in bud tissue volume during the process of deacclimation, but major increases in volume occur after most of the supercooling ability is lost, suggesting growth resumption processes are limited by deacclimation state.

Understanding the phyllosphere microbiome assemblage in grape species (Vitaceae) with amplicon sequence data structures

Impacts of plant genotype on microbial assemblage in the phyllosphere (above-ground parts of plants, which predominantly consists of the set of photosynthetic leaves) of Vitis vinifera cultivars have been studied previously but the impact of grape species (under the grape family Vitaceae) was never investigated. Considering the fact, that the phyllosphere microbiome may have profound effects on host plant health and its performance traits, studying the impact of grape species in microbial taxa structuring in the phyllosphere could be of crucial importance. We performed 16S and ITS profiling (for bacteria and fungi respectively) to access genus level characterization of the microflora present in the leaf phyllosphere of five species within this plant family, sampled in two successive years from the repository situated in the Mediterranean. We also performed α and β-diversity analyses with robust statistical estimates to test the impacts of grape species and growing year, over a two-year period. Our results indicated the presence of complex microbial diversity and assemblages in the phyllosphere with a significant effect of both factors (grape species and growing year), the latter effect is being more pronounced. We also compared separate normalization methods for high-throughput microbiome data-sets followed by differential taxa abundance analyses. The results suggested the predominance of a particular normalization method over others. This also indicated the need for more robust normalization methods to study the differential taxa abundance among groups in microbiome research.

Tempo of gene regulation in wild and cultivated Vitis species shows coordination between cold deacclimation and budbreak

Dormancy release, loss of cold hardiness and budbreak are critical aspects of the annual cycle of deciduous perennial plants. Molecular control of these processes is not fully understood, and genotypic variation may be important for climate adaptation. To gain greater understanding of these processes, single-node cuttings from wild (Vitis amurensis, V. riparia) and cultivated Vitis genotypes (V. vinifera 'Cabernet Sauvignon', 'Riesling') were collected from the vineyard during winter and placed under forcing conditions. Cold hardiness was measured daily, and buds were collected for gene expression analysis until budbreak. Wild Vitis genotypes had faster deacclimation and budbreak than V. vinifera. Temperature-sensing related genes were quickly and synchronously differentially expressed in all genotypes. Significant changes in the pattern of expression changes for eight major metabolic and hormone related pathways were seen across all genotypes. Downregulation of ABA synthesis appears to play an important role in loss of cold hardiness and budbreak in all genotypes. This role was validated through an observed halt in cold hardiness loss of 'Riesling' buds treated with exogenous ABA. The gene expression cascade that occurs during deacclimation and budbreak phenology of fast (wild) and slow (cultivated) grapevines appears coordinated and temporally conserved within these phenotypes.

Multigene phylogeny of root-knot nematodes and molecular characterization of Meloidogyne nataliei Golden, Rose & Bird, 1981 (Nematoda: Tylenchida)

The root-knot nematodes of the genus Meloidogyne are highly adapted, obligate plant parasites, consisting of nearly one hundred valid species, and are considered the most economically important group of plant-parasitic nematodes. Six Meloidogyne species: M. arenaria, M. hapla, M. incognita, M. microtyla, M. naasi and M. nataliei were previously reported in Michigan, USA. For this study, Meloidogyne nataliei was isolated from the grapevine Vitis labrusca from the type locality in Michigan, USA, and was characterized using isozyme analysis and ribosomal and mitochondrial gene sequences. No malate dehydrogenase activity was detected using macerate of one, five, six, seven or ten females of M. nataliei per well. However, one strong band (EST = S1; Rm: 27.4) of esterase activity was detected when using homogenates of ten egg-laying females per well. Phylogenetic analyses of sequences of the partial 18S ribosomal RNA, D2-D3 of 28S rRNA, internal transcribed spacer of rRNA, mitochondrial cytochrome oxidase subunit I genes and the cytochrome oxidase subunit II-16S rRNA intergeneric fragment from fifty-five valid Meloidogyne species and M. nataliei were conducted using Bayesian inference and maximum likelihood methods. From these results, we infer 11 distinct clades among studied species, with M. nataliei and M. indica composing a basal lineage. Seventy five percent of these species belong to seven clades within the Meloidogyne superclade. Characterization of these clades is provided and evolutionary trends within the root-knot nematodes are discussed.

Dates and rates in grape's plastomes: evolution in slow motion

The family Vitaceae includes the domesticated grapevine (Vitis vinifera), one of the most economically important crops in the world. Despite the importance of Vitaceae, there is still considerable controversy surrounding their phylogenetic relationships and evolutionary timescales. Moreover, variation in rates of molecular evolution among Vitaceae remains mostly unexplored. The present research aims to fill these knowledge gaps through the analysis of plastome sequences. Thirteen newly sequenced grape plastomes are presented and their phylogenetic relationships examined. Divergence times and absolute substitution rates are inferred under different molecular clocks by the analysis of 95 non-coding plastid regions and 43 representative accessions of the major lineages of Vitaceae. Furthermore, the phylogenetic informativeness of non-coding plastid regions is investigated. We find strong evidence in favor of the random local clock model and rate heterogeneity within Vitaceae. Substitution rates decelerate in Ampelocissus, Ampelopsis, Nekemias, Parthenocissus, Rhoicissus, and Vitis, with genus Vitis showing the lowest values up to a minimum of ~ 4.65 × 10^-11 s/s/y. We suggest that liana-like species of Vitaceae evolve slower than erect growth habit plants and we invoke the "rate of mitosis hypothesis" to explain the observed pattern of the substitution rates. We identify a reduced set of 20 non-coding regions able to accurately reconstruct the phylogeny of Vitaceae and we provide a detailed description of all 152 non-coding regions identified in the plastomes of subg. Vitis. These polymorphic regions will find their applications in phylogenetics, phylogeography, and population genetics as well in grapes identification through DNA barcoding techniques.

High-density linkage maps and loci for berry color and flower sex in muscadine grape (Vitis rotundifolia)

Linkage maps of muscadine grape generated using genotyping-by-sequencing (GBS) provide insight into genome collinearity between Muscadinia and Euvitis subgenera and genetic control of flower sex and berry color. The muscadine grape, Vitis rotundifolia, is a specialty crop native to the southeastern USA. Muscadine vines can be male, female, or perfect-flowered, and berry color ranges from bronze to black. Genetic linkage maps were constructed using genotyping-by-sequencing in two F₁ populations segregating for flower sex and berry color. The linkage maps consisted of 1244 and 2069 markers assigned to 20 linkage groups (LG) for the 'Black Beauty' × 'Nesbitt' and 'Supreme' × 'Nesbitt' populations, respectively. Data from both populations were used to generate a consensus map with 2346 markers across 20 LGs. A high degree of collinearity was observed between the genetic maps and the Vitis vinifera physical map. The higher chromosome number in muscadine (2n = 40) compared to V. vinifera (2n = 38) was accounted for by the behavior of V. vinifera chromosome 7 as two independently segregating LGs in muscadine. The muscadine sex locus mapped to an interval that aligned to 4.64-5.09 Mb on V. vinifera chromosome 2, a region which includes the previously described V. vinifera subsp. sylvestris sex locus. While the MYB transcription factor genes controlling fruit color in V. vinifera are located on chromosome 2, the muscadine berry color locus mapped to an interval aligning to 11.09-11.88 Mb on V. vinifera chromosome 4, suggesting that a mutation in a different gene in the anthocyanin biosynthesis pathway determines berry color in muscadine. These linkage maps lay the groundwork for marker-assisted breeding in muscadine and provide insight into the evolution of Vitis species.