Abstract
Besides signalling to soil organisms, strigolactones (SLs) control above- and below-ground morphology, in particular shoot branching. Furthermore, SLs interact with stress responses, possibly thanks to a crosstalk with the abscisic acid (ABA) signal. In grapevine (Vitis vinifera L.), ABA drives the accumulation of anthocyanins over the ripening season. In this study, we investigated the effects of treatment with a synthetic strigolactone analogue, GR24, on anthocyanin accumulation in grape berries, in the presence or absence of exogenous ABA treatment. Experiments were performed both on severed, incubated berries, and on berries attached to the vine. Furthermore, we analysed the corresponding transcript concentrations of genes involved in anthocyanin biosynthesis, and in ABA biosynthesis, metabolism, and membrane transport. During the experiment time courses, berries showed the expected increase in soluble sugars and anthocyanins. GR24 treatment had no or little effect on anthocyanin accumulation, or on gene expression levels. Exogenous ABA treatment activated soluble sugar and anthocyanin accumulation, and enhanced expression of anthocyanin and ABA biosynthetic genes, and that of genes involved in ABA hydroxylation and membrane transport. Co-treatment of GR24 with ABA delayed anthocyanin accumulation, decreased expression of anthocyanin biosynthetic genes, and negatively affected ABA concentration. GR24 also enhanced the ABA-induced activation of ABA hydroxylase genes, while it down-regulated the ABA-induced activation of ABA transport genes. Our results show that GR24 affects the ABA-induced activation of anthocyanin biosynthesis in this non-climacteric fruit. We discuss possible mechanisms underlying this effect, and the potential role of SLs in ripening of non-ABA-treated berries.
Highlights
Grapevine ranks fourth among major fruit crops worldwide, and first in Europe
In order to investigate both specific and combined effects of GR24 and abscisic acid (ABA) on ripening of grape berries, we incubated detached berries in vitro on media supplied with sucrose and hormones
Exogenous SL negatively interacts with ABA-induced anthocyanin accumulation in grape berries
Summary
Grapevine ranks fourth among major fruit crops worldwide, and first in Europe (http://www.fao.org/faostat/en/#data). Methyl jasmonate treatments enhance anthocyanin accumulation in suspension cultures (Belhadj et al, 2008) and in whole berries (Jia et al, 2016; Symons et al., 2006) Besides these hormones, abscisic acid (ABA) has been long suspected to be the master controller of ripening in grapevine, as both its biosynthesis (Deluc et al, 2007) and concentration in the berry (Coombe and Hale, 1973; Davies et al, 1997) peak at véraison. Arabidopsis, Lotus, and tomato genotypes with reduced SL levels are hypersensitive to drought stress (Ha et al, 2014; Liu et al, 2015; Lv et al, 2017; Visentin et al, 2016), while SL supplementation abolishes the drought-sensitive genotype In most of these studies, SL-dependent changes in stress susceptibility were mainly linked to an ABA signalling-dependent modulation of stomatal closure, suggesting that strigolactones may interact with the ABA signal upon stress. By application of the SL analogue GR24 (Besserer et al, 2008) to berries at véraison in the presence and absence of exogenous ABA, we demonstrate that exogenous SL down-regulates the effects of exogenous (but not endogenous) ABA, possibly by affecting its metabolism and transport
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