Sugar accumulation and malic acid degradation uncoupled by temperature in microvine berries

Abstract

Global warming has already become a critical problem for wine quality in many viticulture regions. However the developmental and molecular mechanisms involved in the response of the grapevine fruit to temperature remain still very elusive. Field experimentation introduces biases in abiotic stress studies on perennial plants such as the grapevine, due to fluctuating uncontrolled conditions. In addition, un-synchronized berry ripening is a major issue that needs to be addressed in abiotic stress studies to reduce experimental noise. In the present study, several long-term temperature treatments were conducted under precisely controlled conditions, using the microvine (DRCF-mutant) as a model. Fruit development and physiology, and the transcriptome adaptation to heat were monitored both at single berry and population levels. Monitoring of the sugar and organic acid content of single berries illustrates that berry heterogeneity within post-véraison clusters spans from plateau herbacé to early maturity, as usually observed on average clusters sequentially sampled along this developmental period. Temperature studies showed an advanced green berry development at higher temperature followed by faster malic acid breakdown during ripening. For the first time in grapevine, we observed a uncoupling of sugar and malic-acid metabolism at the inception of ripening under low temperature. RNA-seq analyses yielded a total of 10 787 temperature-modulated transcripts supporting a range of physiological functions related to primary metabolism. This work, which is the first abiotic stress study on fleshy fruits using RNA-seq for transcriptomic analysis, provides new clues on the mechanisms underlying the metabolic changes caused by temperature during berry development.