Long-term observations in Napa Valley and Bordeaux reveal that grapevines never reach a lethal level of drought.

SummaryA long-term in vitro culture system of intact grape berries was developed which can serve to study the response of berry composition to various trophic factors, shown by sugar regulation of anthocyanin accumulation.

Light exclusion reduces the concentration and modifies the composition of grape anthocyanins, by altering the expression of genes involved in anthocyanin biosynthesis and transport, in a cultivar- and tissue-specific manner. Unlike most grapes, teinturier grapes accumulate anthocyanins both in skin and flesh. However, the concentration and composition of anthocyanins in both tissues differ, providing a valuable system to study tissue-specific regulation of anthocyanin synthesis. Furthermore, little is known about the mechanisms controlling the sensitivity of anthocyanin accumulation to light. Here, light was excluded from Gamay (white-fleshed) and Gamay Fréaux (teinturier mutant) berries throughout berry development. Under light-exposed conditions, the skin of Gamay Fréaux accumulated the highest level of anthocyanins, followed by the skin of Gamay, while the pulp of Gamay Fréaux had much lower anthocyanins than the skins. Network analysis revealed the same order on the number of significant correlations among metabolites and transcripts in the three colored tissues, indicating a higher connectivity that reflects a higher efficiency of the anthocyanin pathway. Compared to light conditions, light exclusion reduced the total amount of anthocyanins, most severely in the skin of Gamay and to a lesser extent in the flesh and skin of Gamay Fréaux. Coordinated decrease in the transcript abundance of structural, regulatory and transporter genes by light exclusion correlated with the reduced anthocyanin concentration in a cultivar- and tissue-specific manner. Moreover, light exclusion increased the ratio of dihydroxylated to trihydroxylated anthocyanins, in parallel with F3'H and F3'5'H transcript amounts. Sugars and ABA only play a limited role in the control of anthocyanin synthesis in the berries, in contrast with what has been described in cell suspensions. This study provides novel insights into the regulation of anthocyanin in wild type and teinturier cultivars.

BackgroundThe major intrinsic protein (MIP) family is a family of proteins, including aquaporins, which facilitate water and small molecule transport across plasma membranes. In plants, MIPs function in a huge variety of processes including water transport, growth, stress response, and fruit development. In this study, we characterize the structure and transcriptional regulation of the MIP family in grapevine, describing the putative genome duplication events leading to the family structure and characterizing the family’s tissue and developmental specific expression patterns across numerous preexisting microarray and RNAseq datasets. Gene co-expression network (GCN) analyses were carried out across these datasets and the promoters of each family member were analyzed for cis-regulatory element structure in order to provide insight into their transcriptional regulation.ResultsA total of 29 Vitis vinifera MIP family members (excluding putative pseudogenes) were identified of which all but two were mapped onto Vitis vinifera chromosomes. In this study, segmental duplication events were identified for five plasma membrane intrinsic protein (PIP) and four tonoplast intrinsic protein (TIP) genes, contributing to the expansion of PIPs and TIPs in grapevine. Grapevine MIP family members have distinct tissue and developmental expression patterns and hierarchical clustering revealed two primary groups regardless of the datasets analyzed. Composite microarray and RNA-seq gene co-expression networks (GCNs) highlighted the relationships between MIP genes and functional categories involved in cell wall modification and transport, as well as with other MIPs revealing a strong co-regulation within the family itself. Some duplicated MIP family members have undergone sub-functionalization and exhibit distinct expression patterns and GCNs. Cis-regulatory element (CRE) analyses of the MIP promoters and their associated GCN members revealed enrichment for numerous CREs including AP2/ERFs and NACs.ConclusionsCombining phylogenetic analyses, gene expression profiling, gene co-expression network analyses, and cis-regulatory element enrichment, this study provides a comprehensive overview of the structure and transcriptional regulation of the grapevine MIP family. The study highlights the duplication and sub-functionalization of the family, its strong coordinated expression with genes involved in growth and transport, and the putative classes of TFs responsible for its regulation.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4638-5) contains supplementary material, which is available to authorized users.

Phosphorus is essential for plant life and plants have developed numerous strategies to maximise phosphate (Pi) acquisition and use under limited Pi supply. Here we have used reciprocal grafting to determine whether the shoot and root have different roles in regulating some of these strategies.Reciprocal grafts of two grapevine genotypes (Vitis vinifera cv. Pinot noir and V. berlandieri x V. rupestris cv. 1103 Paulsen) were produced as well as the corresponding homo-graft controls; the plants were grown in hydroponic culture and subjected to two levels of Pi supply (high (0.6 mM) or low (0.001 mM)). Biomass accumulation, root morphology, and root, stem and leaf organic acid, phosphate, nitrate and sulphate concentrations were measured. The transcript abundance of orthologues of known phosphate starvation induced (PSI) genes from Arabidopsis was also quantified. Under high Pi, the scion genotype had a large impact on plant growth, but the morphology of roots (such as root tip density) was not affected. Low Pi supply affected growth, tissue organic acid concentration, the activity of acid phosphatases released by the roots and the expression of PSI genes. Rootstock genotypes showed differences in root responses to low Pi supply, but the scion also exerted long-distance regulation of rootstock responses to low Pi, for example, modifying PSI gene expression, sulphate acquisition efficiency, the activity of acid phosphatases released by the roots and root organic acid concentrations. This work shows for the first time that the grapevine genotypes differ in their response to low Pi supply and that the scion can modify rootstock responses to the nutrient availability. This work highlights that genetic variation in shootborne signals can regulate root responses to Pi supply and that understanding rootstock responses to the environment must be done considering scion influence. AG, IM, BP and PD executed the experiments and collected data, AG and NC analysed the data, VL, AM, PV and SJC acquired the funding, SJC drafted the manuscript, and all authors made significant intellectual contributions to the design and execution of the work, and revised the manuscript. ReferencesAttia F, Garcia F, Garcia M, Besnard E, Lamaze T. 2007. Effect of rootstock on organic acids in leaves and berries and on must and wine acidity of two red wine grape cultivars 'Malbec' and 'Négrette' (Vitis vinifera L.) grown hydroponically. Acta Horticulturae 754, 473-482.