Abscisic acid is a major regulator of grape berry ripening onset: new insights into ABA signaling network

The process of grape berry ripening is non climacteric and does not rely on the sole ethylene signal. Abscisic acid (ABA) is recognized as an important hormone of ripening inception and color development in ripening berries. To elucidate the effect of this signal at the molecular level, pre-véraison berries were treated ex-vivo for 20 hours with 0.2 mM ABA and berry skin transcriptional modulation was studied by RNA-seq after the treatment and 24 hours later, in the absence of exogenous ABA. This study highlighted that a small amount of ABA triggered its own biosynthesis and had a transcriptome-wide effect characterized by the amplification of the transcriptional response over time. An extensive overlap with the genes modulated during physiological ripening proved the major role played by ABA in the regulation of berry ripening. The signaling network of ABA, encompassing ABA metabolism, transport and signaling cascade, has been analyzed in detail and expanded based on knowledge from other species. Four candidate genes have been experimentally assayed for their transcriptional regulation by ABA. This knowledge of the ABA cascade in berry skin at ripening onset might be useful to other areas of viticultural interest, such as bud dormancy regulation and drought stress tolerance.