Light-induced Variation in Phenolic Compounds in Cabernet Sauvignon Grapes (Vitis vinifera L.) Involves Extensive Transcriptome Reprogramming of Biosynthetic Enzymes, Transcription Factors, and Phytohormonal Regulators.

Run-Ze Sun,Wen-Feng Song,Yan-Rong Zhu,Yi-Bin Lan,Qiang Li,Xue Zhang,Xiao-Di Cui,Guo Cheng,Yan-Nan He,Yu Wang,Wu Chen,Jun Wang,Si-Yu Li

doi:10.3389/fpls.2017.00547

Abstract

Light environments have long been known to influence grape (Vitis vinifera L.) berry development and biosynthesis of phenolic compounds, and ultimately affect wine quality. Here, the accumulation and compositional changes of hydroxycinnamic acids (HCAs) and flavonoids, as well as global gene expression were analyzed in Cabernet Sauvignon grape berries under sunlight exposure treatments at different phenological stages. Sunlight exposure did not consistently affect the accumulation of berry skin flavan-3-ol or anthocyanin among different seasons due to climatic variations, but increased HCA content significantly at véraison and harvest, and enhanced flavonol accumulation dramatically with its timing and severity degree trend. As in sunlight exposed berries, a highly significant correlation was observed between the expression of genes coding phenylalanine ammonia-lyase, 4-coumarate: CoA ligase, flavanone 3-hydroxylase and flavonol synthase family members and corresponding metabolite accumulation in the phenolic biosynthesis pathway, which may positively or negatively be regulated by MYB, bHLH, WRKY, AP2/EREBP, C2C2, NAC, and C2H2 transcription factors (TFs). Furthermore, some candidate genes required for auxin, ethylene and abscisic acid signal transductions were also identified which are probably involved in berry development and flavonoid biosynthesis in response to enhanced sunlight irradiation. Taken together, this study provides a valuable overview of the light-induced phenolic metabolism and transcriptome changes, especially the dynamic responses of TFs and signaling components of phytohormones, and contributes to the further understanding of sunlight-responsive phenolic biosynthesis regulation in grape berries.

Highlights

Phenolic compounds, mainly hydroxycinnamic acids (HCAs) and flavonoids, are one of the most abundant secondary metabolites in grape (Vitis vinifera L.) berries and important to wine quality
Eight fruit-zone light exposure levels were established in the vines through artificial leaf removal, half leaf removal, or leaf moving (Figure 1): leaf removal at berry pepper-corn size (LR-PS); leaf removal at véraison (LR-V); leaf removal after véraison (LR-AV); half leaf removal at véraison (HLR-V); half leaf removal after véraison (HLR-AV); leaf moving at véraison (LM-V); leaf moving after véraison (LM-AV); and non-treated control (C)
There was no significant difference in the titratable acidity (TA) among treatments in all the three seasons (Supplementary Figure S1), which was inconsistent with previous studies that leaf removal treatments reduced TA (Zoecklein et al, 1992; Percival et al, 1994), suggesting that TA was differently affected by sunlight exposure depending on cultivar and climate

Summary

Introduction

Mainly hydroxycinnamic acids (HCAs) and flavonoids, are one of the most abundant secondary metabolites in grape (Vitis vinifera L.) berries and important to wine quality. PAs, named condensed tannins, are polymers of flavan-3-ol monomeric units (such as catechin, epicatechin, epicatechin-3-O-gallte, and epigallocatechin) which located in both the grape skins and the seeds, with trace amounts accumulated in the vasculature of berries, whereas flavonols and anthocyanins are detected only in berry skins (Downey et al, 2006). All these compounds have important physiological functions in diverse aspects of grape berry development, such as free radical scavenging, pigmentation and co-pigmentation, ultraviolet (UV) radiation protection and defense against microbial and fungal infections (Harborne and Williams, 2000; Winkel-Shirley, 2001). In the case of grapevine, VviMYB4a and its close homolog VviMYB4b have been characterized as important negative regulators of small-weight phenolic biosynthesis, whereas two other repressors, VviMYBC2-L1 and VviMYBC2-L3, were shown to fine tune flavonoid levels (Huang et al, 2014; Cavallini et al, 2015)

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Conclusion