Mapping genetic loci for tolerance to lime-induced iron deficiency chlorosis in grapevine rootstocks (Vitis sp.)

LiDAR Is Effective in Characterizing Vine Growth and Detecting Associated Genetic Loci

The strong societal demand to reduce pesticide use and adaptation to climate change challenges the capacities of phenotyping new varieties in the vineyard. High-throughput phenotyping is a way to obtain meaningful and reliable information on hundreds of genotypes in a limited period. We evaluated traits related to growth in 209 genotypes from an interspecific grapevine biparental cross, between IJ119, a local genitor, and Divona, both in summer and in winter, using several methods: fresh pruning wood weight, exposed leaf area calculated from digital images, leaf chlorophyll concentration, and LiDAR-derived apparent volumes. Using high-density genetic information obtained by the genotyping by sequencing technology (GBS), we detected 6 regions of the grapevine genome [quantitative trait loci (QTL)] associated with the variations of the traits in the progeny. The detection of statistically significant QTLs, as well as correlations (R2) with traditional methods above 0.46, shows that LiDAR technology is effective in characterizing the growth features of the grapevine. Heritabilities calculated with LiDAR-derived total canopy and pruning wood volumes were high, above 0.66, and stable between growing seasons. These variables provided genetic models explaining up to 47% of the phenotypic variance, which were better than models obtained with the exposed leaf area estimated from images and the destructive pruning weight measurements. Our results highlight the relevance of LiDAR-derived traits for characterizing genetically induced differences in grapevine growth and open new perspectives for high-throughput phenotyping of grapevines in the vineyard.

Dissecting the genetic architecture of root-related traits in a grafted wild Vitis berlandieri population for grapevine rootstock breeding

In woody perennial plants, quantitative genetics and association studies remain scarce for root-related traits, due to the time required to obtain mature plants and the complexity of phenotyping. In grapevine, a grafted cultivated plant, most of the rootstocks used are hybrids between American Vitis species (V. rupestris, V. riparia, and V. berlandieri). In this study, we used a wild population of an American Vitis species (V. berlandieri) to analyze the genetic architecture of the root-related traits of rootstocks in a grafted context. We studied a population consisting of 211 genotypes, with one to five replicates each (n = 846 individuals), plus four commercial rootstocks as control genotypes (110R, 5BB, Börner, and SO4). After two independent years of experimentation, the best linear unbiased estimates method revealed root-related traits with a moderate-to-high heritability (0.36-0.82) and coefficient of genetic variation (0.15-0.45). A genome-wide association study was performed with the BLINK model, leading to the detection of 11 QTL associated with four root-related traits (one QTL was associated with the total number of roots, four were associated with the number of small roots (< 1 mm in diameter), two were associated with the number of medium-sized roots (1 mm < diameter < 2 mm), and four were associated with mean diameter) accounting for up to 25.1% of the variance. Three genotypes were found to have better root-related trait performances than the commercial rootstocks and therefore constitute possible new candidates for use in grapevine rootstock breeding programs.

Genetic analysis of grapevine root system architecture and loci associated gene networks

Own-rooted grapevines and grapevine rootstocks are vegetatively propagated from cuttings and have an adventitious root system. Unraveling the genetic underpinnings of the adventitious root system architecture (RSA) is important for improving own-rooted and grafted grapevine sustainability for a changing climate. Grapevine RSA genetic analysis was conducted in an Vitis sp. 'VRS-F2' population. Nine root morphology, three total root system morphology, and two biomass traits that contribute to root anchorage and water and nutrient uptake were phenotyped. Quantitative trait loci (QTL) analysis was performed using a high density integrated GBS and rhAmpSeq genetic map. Thirty-one QTL were detected for eleven of the RSA traits (surface area, root volume, total root length, fresh weight, number of tips, forks or links, longest root and average root diameter, link length, and link surface area) revealing many small effects. Several QTL were colocated on chromosomes 1, 9, 13, 18, and 19. QTL with identical peak positions on chromosomes 1 or 13 were enriched for AP2-EREBP, AS2, C2C2-CO, HMG, and MYB transcription factors, and QTL on chromosomes 9 or 13 were enriched for the ALFIN-LIKE transcription factor and regulation of autophagy pathways. QTL modeling for individual root traits identified eight models explaining 13.2 to 31.8% of the phenotypic variation. 'Seyval blanc' was the grandparent contributing to the allele models that included a greater surface area, total root length, and branching (number of forks and links) traits promoting a greater root density. In contrast, V. riparia 'Manitoba 37' contributed the allele for greater average branch length (link length) and diameter, promoting a less dense elongated root system with thicker roots. LATERAL ORGAN BOUNDARY DOMAIN (LBD or AS2/LOB) and the PROTODERMAL FACTOR (PFD2 and ANL2) were identified as important candidate genes in the enriched pathways underlying the hotspots for grapevine adventitious RSA. The combined QTL hotspot and trait modeling identified transcription factors, cell cycle and circadian rhythm genes with a known role in root cell and epidermal layer differentiation, lateral root development and cortex thickness. These genes are candidates for tailoring grapevine root system texture, density and length in breeding programs.

Rootstock-scion combination contributes to shape diversity and composition of microbial communities associated with grapevine root system

To alleviate biotic and abiotic stresses and enhance fruit yield, many crops are cultivated in the form of grafted plants, in which the shoot (scion) and root (rootstock) systems of different species are joined together. Because (i) the plant species determines the microbial recruitment from the soil to the root and (ii) both scion and rootstock impact the physiology, morphology and biochemistry of the grafted plant, it can be expected that their different combinations should affect the recruitment and assembly of plant microbiome. To test our hypothesis, we investigated at a field scale the bacterial and fungal communities associated with the root system of seven grapevine rootstock–scion combinations cultivated across 10 different vineyards. Following the soil type, which resulted in the main determinant of the grapevine root microbial community diversity, the rootstock–scion combination resulted more important than the two components taken alone. Notably, the microbiome differences among the rootstock–scion combinations were mainly dictated by the changes in the relative abundance of microbiome members rather than by their presence/absence. These results reveal that the microbiome of grafted grapevine root systems is largely influenced by the combination of rootstock and scion, which affects the microbial diversity uptaken from soil.

Identification of SNPs associated with magnesium and sodium uptake and the effect of their accumulation on micro and macro nutrient levels in Vitis vinifera

Macro and micro nutrient accumulation affects all stages of plant growth and development. When nutrient deficiencies or excesses occur, normal plant growth is altered resulting in symptoms such as leaf chlorosis, plant stunting or death. In grapes, few genomic regions associated with nutrient accumulation or deficiencies have been identified. Our study evaluated micro and macro nutrient concentrations in Vitis vinifera L. to identify associated SNPs using an association approach with genotype by sequencing data. Nutrient concentrations and foliar symptoms (leaf chlorosis and stunting) were compared among 249 F₁Vitis vinifera individuals in 2015 and 2016. Foliar symptoms were consistent (≥90%) between years and correlated with changes in nutrient concentrations of magnesium (r = 0.65 and r = 0.38 in 2015 and 2016, respectively), aluminum (r = 0.24 and r = 0.49), iron (r = 0.21 and r = 0.49), and sodium (r = 0.32 and r = 0.21). Single nucleotide polymorphisms associated with symptoms, sodium, and magnesium were detected on each chromosome with the exception of 5, 7 and 17 depending on the trait and genome used for analyses explaining up to 40% of the observed variation. Symptoms and magnesium concentration were primarily associated with SNPs on chromosome 3, while SNPs associated with increased sodium content were primarily found on chromosomes 11 and 18. Mean concentrations for each nutrient varied between years in the population between symptomatic and asymptomatic plants, but relative relationships were mostly consistent. These data suggest a complex relationship among foliar symptoms and micro and macro nutrients accumulating in grapevines.

Selection of candidate genes controlling veraison time in grapevine through integration of meta-QTL and transcriptomic data

BACKGROUND

High temperature during grape berry ripening impairs the quality of fruits and wines. Veraison time, which marks ripening onset, is a key factor for determining climatic conditions during berry ripening. Understanding its genetic control is crucial to successfully breed varieties more adapted to a changing climate. Quantitative trait loci (QTL) studies attempting to elucidate the genetic determinism of developmental stages in grapevine have identified wide genomic regions. Broad scale transcriptomic studies, by identifying sets of genes modulated during berry development and ripening, also highlighted a huge number of putative candidates.

RESULTS

With the final aim of providing an overview about available information on the genetic control of grapevine veraison time, and prioritizing candidates, we applied a meta-QTL analysis for grapevine phenology-related traits and checked for co-localization of transcriptomic candidates. A consensus genetic map including 3130 markers anchored to the grapevine genome assembly was compiled starting from 39 genetic maps. Two thousand ninety-three QTLs from 47 QTL studies were projected onto the consensus map, providing a comprehensive overview about distribution of available QTLs and revealing extensive co-localization especially across phenology related traits. From 141 phenology related QTLs we generated 4 veraison meta-QTLs located on linkage group (LG) 1 and 2, and 13 additional meta-QTLs connected to the veraison time genetic control, among which the most relevant were located on LG 14, 16 and 18. Functional candidates in these intervals were inspected. Lastly, taking advantage of available transcriptomic datasets, expression data along berry development were integrated, in order to pinpoint among positional candidates, those differentially expressed across the veraison transition.

CONCLUSION

Integration of meta-QTLs analysis on available phenology related QTLs and data from transcriptomic dataset allowed to strongly reduce the number of candidate genes for the genetic control of the veraison transition, prioritizing a list of 272 genes, among which 78 involved in regulation of gene expression, signal transduction or development.

Soil carbonate drives local adaptation in Arabidopsis thaliana

High soil carbonate limits crop performance especially in semiarid or arid climates. To understand how plants adapt to such soils, we explored natural variation in tolerance to soil carbonate in small local populations (demes) of Arabidopsis thaliana growing on soils differing in carbonate content. Reciprocal field-based transplants on soils with elevated carbonate (+C) and without carbonate (-C) over several years revealed that demes native to (+C) soils showed higher fitness than those native to (-C) soils when both were grown together on carbonate-rich soil. This supports the role of soil carbonate as a driving factor for local adaptation. Analyses of contrasting demes revealed key mechanisms associated with these fitness differences. Under controlled conditions, plants from the tolerant deme A1(+C) native to (+C) soil were more resistant to both elevated carbonate and iron deficiency than plants from the sensitive T6(-C) deme native to (-C) soil. Resistance of A1(+C) to elevated carbonate was associated with higher root extrusion of both protons and coumarin-type phenolics. Tolerant A1(+C) also had better Ca-exclusion than sensitive T6(-C) . We conclude that Arabidopsis demes are locally adapted in their native habitat to soils with moderately elevated carbonate. This adaptation is associated with both enhanced iron acquisition and calcium exclusion.

Merging genotypes: graft union formation and scion-rootstock interactions

Grafting has been utilised for at least the past 7000 years. Historically, grafting has been developed by growers without particular interest beyond the agronomical and ornamental effects, and thus knowledge about grafting has remained largely empirical. Much of the commercial production of fruit, and increasingly vegetables, relies upon grafting with rootstocks to provide resistance to soil-borne pathogens and abiotic stresses as well as to influence scion growth and performance. Although there is considerable agronomic knowledge about the use and selection of rootstocks for many species, we know little of the molecular mechanisms underlying rootstock adaptation to different soil environments and rootstock-conferred modifications of scion phenotypes. Furthermore, the processes involved in the formation of the graft union and graft compatibility are poorly understood despite over a hundred years of scientific study. In this paper, we provide an overview of what is known about grafting and the mechanisms underlying rootstock-scion interactions. We highlight recent studies that have advanced our understanding of graft union formation and outline subjects that require further development.

Genetic architecture of aerial and root traits in field-grown grafted grapevines is largely independent

QTLs were identified for traits assessed on field-grown grafted grapevines. Root number and section had the largest phenotypic variance explained. Genetic control of root and aerial traits was independent. Breeding new rootstocks for perennial crops remains challenging, mainly because of the number of desirable traits which have to be combined, these traits include good rooting ability and root development. Consequently, the present study analyzes the genetic architecture of root traits in grapevine. A segregating progeny of 138 F1 genotypes issued from an inter-specific cross between Vitis vinifera cv. Cabernet-Sauvignon × V. riparia cv. Gloire de Montpellier, used as rootstock, was phenotyped in grafted plants grown for 2 years in the field. Seven traits, related to aerial and root development, were quantified. Heritability ranged between 0.44 for aerial biomass to 0.7 for root number. Total root number was related to the number of fine roots, while root biomass was related to the number of coarse roots. Significant quantitative trait loci (QTLs) were identified for all the traits studied with some of them explaining approximately 20% of phenotypic variance. Only a single QTL co-localized for root and aerial biomass. Identified QTLs for aerial-to-root biomass ratio suggest that aerial and root traits are controlled independently. Genes known to be involved in auxin signaling pathways and phosphorus nutrition, whose orthologues were previously shown to regulate root development in Arabidopsis, were located in the confidence intervals of several QTLs. This study opens new perspectives for breeding rootstocks with improved root development capacities.

Grapevine rootstocks shape underground bacterial microbiome and networking but not potential functionality

BACKGROUND

The plant compartments of Vitis vinifera, including the rhizosphere, rhizoplane, root endosphere, phyllosphere and carposphere, provide unique niches that drive specific bacterial microbiome associations. The majority of phyllosphere endophytes originate from the soil and migrate up to the aerial compartments through the root endosphere. Thus, the soil and root endosphere partially define the aerial endosphere in the leaves and berries, contributing to the terroir of the fruit. However, V. vinifera cultivars are invariably grafted onto the rootstocks of other Vitis species and hybrids. It has been hypothesized that the plant species determines the microbiome of the root endosphere and, as a consequence, the aerial endosphere. In this work, we test the first part of this hypothesis. We investigate whether different rootstocks influence the bacteria selected from the surrounding soil, affecting the bacterial diversity and potential functionality of the rhizosphere and root endosphere.

METHODS

Bacterial microbiomes from both the root tissues and the rhizosphere of Barbera cultivars, both ungrafted and grafted on four different rootstocks, cultivated in the same soil from the same vineyard, were characterized by 16S rRNA high-throughput sequencing. To assess the influence of the root genotype on the bacterial communities' recruitment in the root system, (i) the phylogenetic diversity coupled with the predicted functional profiles and (ii) the co-occurrence bacterial networks were determined. Cultivation-dependent approaches were used to reveal the plant-growth promoting (PGP) potential associated with the grafted and ungrafted root systems.

RESULTS

Richness, diversity and bacterial community networking in the root compartments were significantly influenced by the rootstocks. Complementary to a shared bacterial microbiome, different subsets of soil bacteria, including those endowed with PGP traits, were selected by the root system compartments of different rootstocks. The interaction between the root compartments and the rootstock exerted a unique selective pressure that enhanced niche differentiation, but rootstock-specific bacterial communities were still recruited with conserved PGP traits.

CONCLUSION

While the rootstock significantly influences the taxonomy, structure and network properties of the bacterial community in grapevine roots, a homeostatic effect on the distribution of the predicted and potential functional PGP traits was found.

Iron deficiency stimulates anthocyanin accumulation in grapevine apical leaves

Iron chlorosis is a diffuse disorder affecting Mediterranean vineyards. Beside the commonly described symptom of chlorophyll decrease, an apex reddening was recently observed. Secondary metabolites, such as anthocyanins, are often synthetized to cope with stresses in plants. The present work aimed to evaluate grapevine responses to iron deficiency, in terms of anthocyanin metabolism (reflectance spectrum, total anthocyanin content, HPLC profile and gene expression) in apical leaves of Cabernet sauvignon and Sangiovese grown in hydroponic conditions. Iron supply interruption produced after one month an increasing of anthocyanin content associated to a more stable profile in both cultivars. In Cabernet sauvignon, the higher red pigment accumulation was associated to a lower intensity of chlorotic symptoms, while in Sangiovese, despite the activation of the metabolism, the lower anthocyanin accumulation was associated to a stronger decrease in chlorophyll concentration. Gene expression data showed a significant increase of anthocyanin biosynthesis. The effects on the expression of structural and transcription factor genes of phenylpropanoid pathway were cultivar dependent. F3H, F3'H, F3'5'H and LDOX genes, in Cabernet sauvignon, and AOMT1 and AOMT genes, in Sangiovese, were positively affected by the treatment in response to iron deficiency. All data support the hypothesis of an anthocyanin biosynthesis stimulation rather than a decreased degradation of them due to iron chlorosis.

Insights into Resistance to Fe Deficiency Stress from a Comparative Study of In Vitro-Selected Novel Fe-Efficient and Fe-Inefficient Potato Plants

Iron (Fe) deficiency induces chlorosis (IDC) in plants and can result in reduced plant productivity. Therefore, development of Fe-efficient plants is of great interest. To gain a better understanding of the physiology of Fe-efficient plants, putative novel plant variants were regenerated from potato (Solanum tubersosum L. var. 'Iwa') callus cultures selected under Fe deficient or low Fe supply (0-5 μM Fe). Based on visual chlorosis rating (VCR), 23% of callus-derived regenerants were classified as Fe-efficient (EF) and 77% as Fe-inefficient (IFN) plant lines when they were grown under Fe deficiency conditions. Stem height was found to be highly correlated with internodal distance, leaf and root lengths in the EF plant lines grown under Fe deficiency conditions. In addition, compared to the IFN plant lines and control parental biotype, the EF plants including the lines named A1, B2, and B9, exhibited enhanced formation of lateral roots and root hairs as well as increased expression of ferritin (fer3) in the leaf and iron-regulated transporter (irt1) in the root. These morphological adaptations and changes in expression the fer3 and irt1 genes of the selected EF potato lines suggest that they are associated with resistance to low Fe supply stress.

Rootstocks: Diversity, Domestication, and Impacts on Shoot Phenotypes

Grafting is an ancient agricultural practice that joins the root system (rootstock) of one plant to the shoot (scion) of another. It is most commonly employed in woody perennial crops to indirectly manipulate scion phenotype. While recent research has focused on scions, here we investigate rootstocks, the lesser-known half of the perennial crop equation. We review natural grafting, grafting in agriculture, rootstock diversity and domestication, and developing areas of rootstock research, including molecular interactions and rootstock microbiomes. With growing interest in perennial crops as valuable components of sustainable agriculture, rootstocks provide one mechanism by which to improve and expand woody perennial cultivation in a range of environmental conditions.

Identification of stable QTLs for vegetative and reproductive traits in the microvine (Vitis vinifera L.) using the 18 K Infinium chip

BACKGROUND

The increasing temperature associated with climate change impacts grapevine phenology and development with critical effects on grape yield and composition. Plant breeding has the potential to deliver new cultivars with stable yield and quality under warmer climate conditions, but this requires the identification of stable genetic determinants. This study tested the potentialities of the microvine to boost genetics in grapevine. A mapping population of 129 microvines derived from Picovine x Ugni Blanc flb, was genotyped with the Illumina® 18 K SNP (Single Nucleotide Polymorphism) chip. Forty-three vegetative and reproductive traits were phenotyped outdoors over four cropping cycles, and a subset of 22 traits over two cropping cycles in growth rooms with two contrasted temperatures, in order to map stable QTLs (Quantitative Trait Loci).

RESULTS

Ten stable QTLs for berry development and quality or leaf area were identified on the parental maps. A new major QTL explaining up to 44 % of total variance of berry weight was identified on chromosome 7 in Ugni Blanc flb, and co-localized with QTLs for seed number (up to 76 % total variance), major berry acids at green lag phase (up to 35 %), and other yield components (up to 25 %). In addition, a minor QTL for leaf area was found on chromosome 4 of the same parent. In contrast, only minor QTLs for berry acidity and leaf area could be found as moderately stable in Picovine. None of the transporters recently identified as mutated in low acidity apples or Cucurbits were included in the several hundreds of candidate genes underlying the above berry QTLs, which could be reduced to a few dozen candidate genes when a priori pertinent biological functions and organ specific expression were considered.

CONCLUSIONS

This study combining the use of microvine and a high throughput genotyping technology was innovative for grapevine genetics. It allowed the identification of 10 stable QTLs, including the first berry acidity QTLs reported so far in a Vitis vinifera intra-specific cross. Robustness of a set of QTLs was assessed with respect to temperature variation.

Ups and downs of a transcriptional landscape shape iron deficiency associated chlorosis of the maize inbreds B73 and Mo17

BACKGROUND

Improving nutrient homeostasis is a major challenge of a sustainable maize cultivation, and cornerstone to ensure food supply for a growing world population. Although, iron constitutes an important nutrient, iron availability is limited. In this respect, iron deficiency associated chlorosis causes severe yield losses every year. Natural variation of the latter trait has yet not been addressed in maize and was therefore studied in the present analysis.

RESULTS

In this study, we i) report about the contrasting chlorosis phenotypes of the inbreds B73 and Mo17 at 10 and 300 μM iron regime, ii) identified over 400 significantly regulated transcripts (FDR < 0.05) within both inbreds at these growth conditions by deep RNA-Sequencing, iii) linked the gained knowledge with QTL information about iron deficiency related traits within the maize intermated B73 by Mo17 (IBM) population, and iv) highlighted contributing molecular pathways. In this respect, several genes within methionine salvage pathway and phytosiderophore synthesis were found to present constitutively high expression in Mo17, even under sufficient iron supply. Moreover, the same expression pattern could be observed for two putative bHLH transcription factors. In addition, a number of differentially expressed genes showed a co-localisation with QTL confidence intervals for iron deficiency related traits within the IBM population.

CONCLUSIONS

Our study highlights differential iron deficiency associated chlorosis between B73 and Mo17 and represents a valuable resource for differentially expressed genes upon iron limitation and chlorosis response. Besides identifying two putative bHLH transcription factors, we propose that methionine salvage pathway and sterol metabolism amongst others; underlie the contrasting iron deficiency related chlorosis phenotype of both inbreds. Altogether, this study emphasizes a contribution of selected genes and pathways on natural trait variation within the IBM population.