STRIGOLACTONES INTERACT WITH ABA-REGULATED ANTHOCYANIN ACCUMULATION IN THE GRAPE BERRY

Berry development is a complex process that can be represented with two successive sigmoid curves from anthesis to ripening, and is divided into three phases. The latter starts after veráison and is known as ripening. It is the phase when many aroma precursors and aromatic compounds are synthetized, and when berries of coloured varieties of grapevine (Vitis vinifera L.) accumulate anthocyanins. Abscisic acid (ABA) plays a crucial role in regulating the accumulation of these compounds in grape berries during ripening. ABA cross-talks with strigolactones (SL) in Arabidopsis, Lotus japonicus and tomato, especially during drought and osmotic stress; therefore in this study, we tested whether and how such an interaction occurs and can affect anthocyanin accumulation in the ripening grape berry. Experiments were performed in vitro (agar plate-incubation of berries collected at the beginning of ripening) and in vivo (by spraying the berries on vines in the vineyard). In both cases, berries were treated at veráison with different combinations of ABA and GR24 (a synthetic SL). Berry skins were used for quantification of anthocyanins, hormones and gene transcripts (by spectrophotometer, UPLC–MS/MS and RT-qPCR, respectively). In both experiments (in vitro and in vivo), anthocyanin quantification and colour variation of berry skins confirmed that ABA stimulates anthocyanin accumulation as expected; however, this process was negatively affected by treatment with GR24. Furthermore, transcripts of genes typically involved in anthocyanin biosynthesis (such as UFGT, MybA1) and ABA concentration levels followed the pattern observed for anthocyanin accumulation. These results support the hypothesis that ABA-induced anthocyanin accumulation in grape berries is inhibited by exogenous SL. However, SL treatment did not alter significantly the transcription of ABA biosynthetic genes. As it is well known that ABA levels are influenced not only by its biosynthesis, but also by its catabolism and transport, we are currently investigating at what level GR24 acts, by profiling the expression of some putative ABA transporter (ABCG-22,-25,-40) and catabolic genes (ABA 8’-hydroxylase) in treated berries.