BackgroundGlobal climate change will noticeably affect plant vegetative and reproductive development. The recent increase in temperatures has already impacted yields and composition of berries in many grapevine-growing regions. Physiological processes underlying temperature response and tolerance of the grapevine fruit have not been extensively investigated. To date, all studies investigating the molecular regulation of fleshly fruit response to abiotic stress were only conducted during the day, overlooking possible critical night-specific variations. The present study explores the night and day transcriptomic response of grapevine fruit to heat stress at several developmental stages. Short heat stresses (2 h) were applied at day and night to vines bearing clusters sequentially ordered according to the developmental stages along their vertical axes. The recently proposed microvine model (DRCF-Dwarf Rapid Cycling and Continuous Flowering) was grown in climatic chambers in order to circumvent common constraints and biases inevitable in field experiments with perennial macrovines. Post-véraison berry heterogeneity within clusters was avoided by constituting homogenous batches following organic acids and sugars measurements of individual berries. A whole genome transcriptomic approach was subsequently conducted using NimbleGen 090818 Vitis 12X (30 K) microarrays.ResultsPresent work reveals significant differences in heat stress responsive pathways according to day or night treatment, in particular regarding genes associated with acidity and phenylpropanoid metabolism. Precise distinction of ripening stages led to stage-specific detection of malic acid and anthocyanin-related transcripts modulated by heat stress. Important changes in cell wall modification related processes as well as indications for heat-induced delay of ripening and sugar accumulation were observed at véraison, an effect that was reversed at later stages.ConclusionsThis first day - night study on heat stress adaption of the grapevine berry shows that the transcriptome of fleshy fruits is differentially affected by abiotic stress at night. The present results emphasize the necessity of including different developmental stages and especially several daytime points in transcriptomic studies.

BackgroundThe 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).ResultsTen 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.ConclusionsThis 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0588-0) contains supplementary material, which is available to authorized users.

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<p class="Abstract" style="text-align: justify;"><strong>Aim:</strong> In the long term, genetic improvement is one of the major strategies to support sustainable wine production in a changing climate. Over the past 5 years, we have developed an interdisciplinary research program that aimed to: i) characterize the impact of temperature increase sensed by the entire plant or individual bunches on the development and functioning of the plant, ii) identify the physiological and molecular mechanisms regulating the response of vegetative and reproductive development to heat stress and iii) develop tools to map quantitative trait loci (QTLs) of plant and berry development in duly controlled, stable, and contrasting environmental conditions.</p><p class="Abstract" style="text-align: justify;"><strong>Methods and results:</strong> Performing high-throughput genomic analyses combined with the use of innovative experimental designs (fruiting cuttings, microvines, single berry sampling) was critical to decipher the ecophysiological and molecular mechanisms involved in the vine response to high temperature.</p><p class="Abstract" style="text-align: justify;"><strong>Conclusion:</strong> Warming promotes vegetative growth and hampers plant carbon balance, disturbing flower set and young berry development. High temperatures modify primary and secondary fruit metabolisms, desynchronizing sugar and organic acid metabolisms and delaying sugar and polyphenol accumulation during ripening. The study of day and night transcriptomic and proteomic signatures associated with heat highlighted key players of the response to temperature in the fruit. </p><p class="Abstract" style="text-align: justify;"><strong>Significance and impact of the study:</strong> Capitalizing on this knowledge, a new program is being proposed for the selection of cultivars limiting the accumulation of sugars in the berry while maintaining other qualitative compounds.</p>