Water limitation and rootstock genotype interact to alter grape berry metabolism through transcriptome reprogramming

Grapevine is a perennial crop often cultivated by grafting a scion cultivar on a suitable rootstock.Rootstocks influence scions,particularly with regard to water uptake and vigor.Therefore,one of the possibilities to adapt viticulture to the extended drought stress periods is to select rootstocks conferring increased tolerance to drought.However,the molecular mechanisms associated with the ability of rootstock/scion combination to influence grape berry metabolism under drought stress are still poorly understood.The transcriptomic changes induced by drought stress in grape berries(cv.Pinot noir)from vines grafted on either 110R(drought-tolerant)or 125AA(drought-sensitive)rootstock were compared.The experiments were conducted in the vineyard for two years and two grape berry developmental stages(50%and 100%veraison).The genome-wide microarray approach showed that water stress strongly impacts gene expression in the berries,through ontology categories that cover cell wall metabolism,primary and secondary metabolism,signaling,stress,and hormones,and that some of these effects strongly depend on the rootstock genotype.Indeed,under drought stress,berries from vines grafted on 110R displayed a different transcriptional response compared to 125AA-concerning genes related to jasmonate(JA),phenylpropanoid metabolism,and pathogenesis-related proteins.The data also suggest a link between JA and secondary metabolism in water-stressed berries.Overall,genes related to secondary metabolism and JA are more induced and/or less repressed by drought stress in the berries grafted on the drought-sensitive rootstock 125AA.These rootstock-dependent gene expression changes are relevant for berry composition and sensory properties.

The role of auxin during early berry development in grapevine as revealed by transcript profiling from pollination to fruit set

Auxin is a key phytohormone that modulates fruit formation in many fleshy fruits through the regulation of cell division and expansion.Auxin content rapidly increases after pollination and the manipulation in its levels may lead to the parthenocarpic development.ln Vitis vinifera L.,little is known about the early fruit development that encompasses from pollination to fruit set.Pollination/fertilization events trigger fruit formation,and auxin treatment mimics their effect in grape berry set.However,the role of auxin in this process at the molecular level is not well understood.To elucidate the participation of auxin in grapevine fruit formation,morphological,reproductive,and molecular events from anthesis to fruit set were described in sequential days after pollination.Exploratory RNA-seq analysis at four time points from anthesis to fruit set revealed that the highest percentage of genes induced/repressed within the hormone-related gene category were auxin-related genes.Transcript profiling showed significant transcript variations in auxin signaling and homeostasis-related genes during the early fruit development.Indole acetic acid and several auxin metabolites were present during this period.Finally,application of an inhibitor of auxin action reduced cell number and the mesocarp diameter,similarly to unpollinated berries,further confirming the key role of auxin during early berry development.This work sheds light into the molecular features of the initial fruit development and highlights the auxin participation during this stage in grapevine.

The Basic Helix-Loop-Helix Transcription Factor MYC1 Is Involved in the Regulation of the Flavonoid Biosynthesis Pathway in Grapevine

Previous results indicated that in grapevine （Vitis vinifera）, regulation of the flavonoid pathway genes by MYB transcription factors depends on their interaction with basic helix-loop-helix proteins （bHLHs）. The present study describes the first functional characterization of a bHLH factor from grapevine named VvMYC1. This transcription factor is phylogenetically related to Arabidopsis bHLH proteins, which participate in the control of flavonoid biosynthesis and epidermal cell fate. Transient promoter and yeast two-hybrid assays demonstrated that VvMYC1 physically interacts with MYB5a, MYB5b, MYBA1/A2, and MYBPA1 to induce promoters of flavonoid pathway genes involved in anthocyanin and/ or proanthocyanidin （PA） synthesis. Additionally, transient promoter assays revealed that VvMYC1 is involved in feedback regulation of its own expression. Transcript levels of VvMYC1 during berry development correlate with the synthesis of anthocyanins and PAs in skins and seeds of berries, suggesting that VvMYC1 is involved in the regulation of anthocyanins and PA synthesis in these organs. Likewise, transient expression of VvMYC1 and VvMYBA1 induces anthocyanin synthesis in grapevine suspension cells. These results suggest that VvMYCl is part of the transcriptional cascade controlling antho- cyanin and PA biosynthesis in grapevine.

Proteomic and metabolomic profiling underlines the stage- and time-dependent effects of high temperature on grape berry metabolism

Climate change scenarios predict an increase in mean air temperatures and in the frequency,intensity,and length of extreme temperature events in many wine-growing regions worldwide.Because elevated temperature has detrimental effects on berry growth and composition,it threatens the economic and environmental sustainability of wine production.Using Cabernet Sauvignon fruit-bearing cuttings,we investigated the effects of high temperature(HT)on grapevine berries through a label-free shotgun proteomic analysis coupled to a complementary metabolomic study.Among the 2,279 proteins identified,592 differentially abundant proteins were found in berries exposed to HT.The gene ontology categories“stress,”“protein,”“secondary metabolism,”and“cell wall”were predominantly altered under HT.High temperatures strongly impaired carbohydrate and energy metabolism,and the effects depended on the stage of development and duration of treatment.Transcript amounts correlated poorly with protein expression levels in HT berries,highlighting the value of proteomic studies in the context of heat stress.Furthermore,this work reveals that HT alters key proteins driving berry development and ripening.Finally,we provide a list of differentially abundant proteins that can be considered as potential markers for developing or selecting grape varieties that are better adapted to warmer climates or extreme heat waves.