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Effects of moderately elevated temperature on grape berry at metabolic and transcriptomic levels

Abstract : Viticulture depends on climate conditions during the growing season. In the context of global warming, any changes in viticulture caused by the rising temperatures expected for the next decades may alter the geographical distribution of grape varieties and even threaten the sustainability of viticulture in hot areas. The objective of this research was to investigate the effects of moderately elevated temperature on grape composition, both at metabolic and transcriptomic levels. A passive open-top heating system was applied in Cabernet Sauvignon (CS) and Sauvignon Blanc (SB) vines grown with standard practice in Bordeaux, France and the Barossa Valley, Australia (CS only) to increase the bunch zone mean temperature by around 0.5-1.6 °C, which was commensurate with the projected global warming. This moderate heating was applied from fruit-set to two weeks after harvest. Metabolites related to technical, phenolic and aromatic maturities (IBMP, the green pepper aroma, precursors of 3SH, grapefruit aroma, and β-damascenone, floral aroma) were assessed, together with transcriptome analysis via RNA-seq and q-PCR, in order to obtain a comprehensive view of berry responses to this moderately elevated temperature in realistic vineyard conditions.The moderately elevated temperature hardly affected the concentrations of sugars, organic acids and total amino acids, but it altered free amino acid composition depending on varieties, vintages and locations.The final concentrations of IBMP were not affected by warming condition in mature berries. However, the elevated temperature significantly reduced IBMP content and expression level of VviOMT3 (a known key gene of IBMP) in CS berries at bunch closure stage, while it reduced the expression levels of VviOMT3 and VviOMT4 at bunch closure stage without affecting IBMP concentration in SB berries. This limited and genotype-dependent effect of elevated temperature suggests that a moderate temperature elevation may not be sufficient to significantly modify IBMP.Glut-3SH-Al was much more concentrated than Glut-3SH and Cys-3SH. Reduced Glut-3SH-Al and Cys-3SH concentrations were associated with a significantly lower expression level of VviGST4 in heated SB berries. Meanwhile, VIT_08s0007g01420 (GSTU8), was down-regulated by elevated temperature and might be a potential candidate gene involved in the biosynthesis of precursors of 3SH.The concentrations of total carotenoids and two predominant carotenoids (lutein and β-carotene) were not altered by elevated temperature in CS berries, but zeaxanthin was reduced by elevated temperature and was significantly less concentrated at harvest. This lower concentration may limit the biosynthesis of β-damascenone and explain the observed lower β-damascenone concentration in post-ripening berries under elevated temperature.A total of 357 genes were differentially expressed (DEGs) in response to the elevated temperature in Bordeaux samples in 2015. Enrichment analysis of Gene Ontology showed that temperature mainly regulated four GO categories, including microtubule, cell wall, extracellular region, and transcription factor activity. 6 DEGs related to anthocyanins synthesis were down-regulated and it could explain, at least in part, the observed lower total anthocyanins in warmed CS. Conversely, tannins were not affected by elevated temperature.The results provide a better understanding of potential global warming effects on metabolite changes during berry development, along with novel molecular insights into the response of grape berry to moderate heating in vineyard conditions.
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Jing Wu. Effects of moderately elevated temperature on grape berry at metabolic and transcriptomic levels. Vegetal Biology. Université de Bordeaux, 2018. English. ⟨NNT : 2018BORD0013⟩. ⟨tel-02018637⟩

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