Dissecting the biochemical and transcriptomic effects of locally applied heat stress on developing Cabernet Sauvignon grape berries. Vitis vinifera

Studying the effect of varying durations (1, 7 and 14 days) of locally applied heat stress on grape berries at three developmental stages (middle green, veraison and middle ripening). Among various environmental factors, temperature is a major regulator affecting plant growth, development and fruit composition. Reproductive development of grapevine and berry composition, are both highly influenced by temperature. To date, the molecular mechanisms involved in grapevine berries tolerance to high temperatures (HS) are poorly understood. Although recent data addressed the consequences on berry development of elevated temperatures applied at the whole plant level, the present work particularly focuses on the fruit responses triggered by direct exposure to heat stress. In the context of climate change, this work focused on microclimate effect is of particular interest to better understand the consequences of leaf removal (a common viticultural practice) on berry development. HS (+ 8°C) was locally applied to clusters from Cabernet Sauvignon fruiting cuttings at three different developmental stages (middle green, véraison and middle ripening). Samples were collected 1, 7 and 14 days after treatment and used for metabolic and transcriptomic analyses. The results showed dramatic and specific biochemical and transcriptomic changes in heat exposed berries, depending on the developmental stage and the stress duration. When applied at the herbaceous stage, HS delayed the onset of véraison. Heating also strongly altered the berry concentration of amino acids and organic acids (e.g. PHE, GABA, and malate) and decreased the anthocyanin content at maturity. These physiological alterations could be partly explained by the deep remodelling of transcriptome in heated berries. More than 7000 genes were deregulated in at least one of the nine experimental conditions. The most affected processes belong to the categories “stress responses”, “protein metabolism” and “secondary metabolisms”, highlighting the intrinsic capacity of grape berries to perceive heat stress and to build adaptive responses. Additionally, important changes in processes related to “transport”, “hormone” and “transcription” might contribute to the postponing of véraison. Finally, opposite effects depending on heating duration were observed for genes encoding enzymes of the general phenylpropanoid pathway, suggesting that the HS-induced decrease in anthocyanin content may result from a combination of transcript abundance and product degradation. Overall design: 54 samples; three developmental stages; heat stress and control for 3 timepoints at each stage; 3 replicates per sample.

本研究探讨了局部施加热应激（heat stress, HS）的不同时长（1、7、14天）对处于三个发育阶段（绿果中期、转色期（véraison）、成熟中期）的葡萄浆果的影响。
在诸多环境因子中，温度是调控植物生长、发育及果实品质组成的核心因子。葡萄的生殖发育与浆果品质组成均受温度的显著调控。
截至目前，学界对葡萄浆果耐受高温热应激的分子机制尚知之甚少。尽管已有研究探讨了整株植株施加高温对浆果发育的影响，但本研究着重聚焦于葡萄果实直接暴露于热应激所引发的响应机制。
在气候变化的大背景下，本研究聚焦微气候效应，旨在更深入理解摘叶（葡萄栽培中的常见农艺措施）对浆果发育的影响。
本研究对处于三个不同发育阶段（绿果中期、转色期（véraison）、成熟中期）的赤霞珠（Cabernet Sauvignon）扦插结果枝的果穗施加了8℃升温的局部热应激处理。
分别于处理后1、7、14天采集样本，用于代谢组学（metabolomic）与转录组学（transcriptomic）分析。
研究结果显示，受热应激的浆果会出现显著且具有特异性的生化与转录组学变化，且变化模式取决于浆果的发育阶段与热应激时长。
在绿果阶段施加热应激时，会延缓转色期的启动。
热应激处理还显著改变了浆果中氨基酸与有机酸的含量（如苯丙氨酸（PHE）、γ-氨基丁酸（GABA）及苹果酸（malate）），并降低了成熟浆果的花青素（anthocyanin）含量。
这些生理变化可部分归因于受热浆果中转录组的深度重塑。
在9种实验条件中的至少1种条件下，共有超过7000个基因的表达出现失调。
受影响最显著的生物学过程集中于“应激响应”“蛋白质代谢”与“次级代谢”类别，这凸显了葡萄浆果感知热应激并构建适应性响应的内在能力。
此外，与“物质转运”“激素调控”及“转录调控”相关的生物学过程出现的显著变化，可能是转色期延迟的重要诱因。
最后，编码苯丙烷通用通路（phenylpropanoid pathway）酶类的基因的表达变化随热应激时长呈现出相反的调控趋势，这表明热应激诱导的花青素含量降低，可能是转录丰度变化与产物降解共同作用的结果。
实验总体设计：共54份样本；涵盖3个发育阶段；每个阶段设置热应激与对照组，并设置3个采样时间点；每个样本设置3次生物学重复。