Dissecting the Biochemical and Transcriptomic Effects of a Locally Applied Heat Treatment on Developing Cabernet Sauvignon Grape Berries

Abstract

Reproductive development of grapevine and berry composition are both strongly influenced by temperature. To date, the molecular mechanisms involved in grapevine berries response to high temperatures are poorly understood. Unlike recent data that addressed the effects 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 treatment (HT). In the context of climate change, this work focusing on temperature effect at the microclimate level is of particular interest as it can help to better understand the consequences of leaf removal (a common viticultural practice) on berry development. HT (+ 8°C) was locally applied to clusters from Cabernet Sauvignon fruiting cuttings at three different developmental stages (middle green, veraison 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, HT delayed the onset of veraison. Heating also strongly altered the berry concentration of amino acids and organic acids (e.g., phenylalanine, γ-aminobutyric acid and malate) and decreased the anthocyanin content at maturity. These physiological alterations could be partly explained by the deep remodeling 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 metabolism,” highlighting the intrinsic capacity of grape berries to perceive HT and to build adaptive responses. Additionally, important changes in processes related to “transport,” “hormone” and “cell wall” might contribute to the postponing of veraison. Finally, opposite effects depending on heating duration were observed for genes encoding enzymes of the general phenylpropanoid pathway, suggesting that the HT-induced decrease in anthocyanin content may result from a combination of transcript abundance and product degradation.

Review of water deficit mediated changes in vine and berry physiology; Consequences for the optimization of irrigation strategies

“…As such Gaiotti et al (2018) emphasize the beneficial effects of cool nights on anthocyanins accumulation. Similar results were obtained by transcriptomic heat stress studies that showed that high temperature is unfavorable for anthocyanin synthesis (Lecourieux et al, 2017;Rienth et al, 2014b;Rienth et al, 2016). Interestingly such effects are most pronounced during the short (24h lasting) véraison phase, where the berry seems to be most vulnerable to abiotic stresses (Rienth et al, 2014b).…”

Single and cumulative effects of whole-vine heat events on Shiraz berry composition

“…Finally, no effects on anthocyanin concentration and profile were found as biosynthesis was not yet triggered in the berries when HE1 was applied. This is in agreement with other studies on Cabernet Sauvignon reporting that anthocyanins were not affected by high temperature when applied during early berry development (Buttrose et al, 1971;Lecourieux et al, 2017).…”

“…Several experiments have already studied berry development and/or metabolite accumulation, but most short-term whole-vine heating treatments were under limited ultra-violet (UV) radiations, e.g. polycarbonate enclosures Sweetman et al, 2014), in growth chambers without UV supplement (Greer and Weston, 2010;Sweetman et al, 2014) or in green houses built with glass or plastic filtering most natural light and UV (Lecourieux et al, 2017;Majer and Hideg, 2012;Pillet, 2011). Systems allowing a more natural UV environment such as open-top chambers have been developed, but have mainly been used to study an increase in long-term average temperature (+ 1-3°C) during several months or the whole grape growing season de Rosas et al, 2017;Sadras and Soar, 2009).…”

Regulation of phytochemicals in fruits and berries by environmental variation—Sugars and organic acids

“…While such treatment during 10–20 weeks after anthesis reduced the amount of incoming photosynthate partitioned to citrate and increased that allocated to sucrose in fruits. Lecourieux et al () reported a significant decrease in the content of malic acid in grape ( Vitis vinifera L. cv. Cabernet Sauvignon) as heat treatment was applied on bunches during stage of either veraison (50% of berries turning to a visible red color) or middle‐ripening (80 days after fruit set), but no impact in its concentration in those heated as stage of middle‐green (30 days after fruit set) was recognized.…”