VviRafS5 Is a Raffinose Synthase Involved in Cold Acclimation in Grapevine Woody Tissues.

Henrique Noronha,Sarah Frusciante,Gianfranco Diretto,Tiago Silva,Hernâni Gerós,Angélica Silva

doi:10.3389/fpls.2021.754537

Abstract

The accumulation of raffinose family oligosaccharides (RFOs) is a hallmark of plant response to different abiotic stresses, including cold. The synthesis of galactinol, by galactinol synthases (GolS), and raffinose, by raffinose synthases (RafS), are fundamental for stress-induced accumulation of RFOs, but the role of these enzymes in the cold response of grapevine (Vitis vinifera L.) woody tissues is still unclear. To address this gap in the literature, 1-year-lignified grapevine canes were incubated at 4°C for 7 and 14 days and tissues were analyzed for sugar content and gene expression. Results showed that, in parallel to starch breakdown, there was an increase in soluble sugars, including sucrose, glucose, fructose, raffinose, and stachyose. Remarkably, abscisic acid (ABA) levels increased during cold acclimation, which correlated with the increased expression of the key ABA-synthesis genes VviNCED2 and VviNCED3. Expression analysis of the VviGolS and VviRafS family allowed the identification of VviRafS5 as a key player in grapevine cold response. The overexpression of VviRafS5 in Saccharomyces cerevisiae allowed the biochemical characterization of the encoded protein as a raffinose synthase with a size of ~87 kDa. In grapevine cultured cells, VviRafS5 was upregulated by cold and ABA but not by heat and salt stresses. Our results suggest that ABA accumulation in woody tissues during cold acclimation upregulates VivRafS5 leading to raffinose synthesis.

Highlights

Among different environmental conditions, low temperature (0–15°C) is the one that mostly affects the geographic distribution of plants, productivity, and yield quality (Thomashow, 1999; Yamaguchi-Shinozaki and Shinozaki, 2006)
This is the case of grapevine (Vitis vinifera L.) that grows primarily in temperate and subtropical regions, whose productivity may be severely affected by environmental fluctuations (Bock et al, 2013)
Cold acclimation is a physiological process leading to freezing tolerance in plants, which is critical for their ability to withstand harsh winter conditions (Thomashow, 1999; Theocharis et al, 2012)

Summary

INTRODUCTION

Low temperature (0–15°C) is the one that mostly affects the geographic distribution of plants, productivity, and yield quality (Thomashow, 1999; Yamaguchi-Shinozaki and Shinozaki, 2006) This is the case of grapevine (Vitis vinifera L.) that grows primarily in temperate and subtropical regions, whose productivity may be severely affected by environmental fluctuations (Bock et al, 2013). Reports have shown that grapevine synthesizes proline and phenolic compounds and accumulates starch and soluble sugars to overcome cold stress (Ait Barka et al, 2006; Fernandez et al, 2012), but there is still a gap of knowledge concerning the role of RFOs in plant adaptation to cold. VviGolS1 was associated with the response to heat stress by synthesizing galactinol, the accumulation of raffinose or stachyose was not detected (Pillet et al, 2012). VviRafS5 is upregulated by cold and ABA but not by heat and salt stresses as observed in grapevine cell suspensions

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DATA AVAILABILITY STATEMENT