Transcriptional analysis of the early ripening of 'Summer Black' grape in response to abscisic acid treatment

Berry quality and harvesting time affect grape (Vitis vinifera L.) market values. Abscisic acid (ABA) applications improve fruit quality and hasten ripening in grapes. However, the molecular mechanisms behind these promotive effects, especially ripening acceleration, remain unclear. Here, treatments of different ABA concentrations were applied to 'Summer Black' grape from ve & PRIME;raison onwards. The ABA applications accelerated berry ripening and improved quality attributes, such as increased sugar and anthocyanin accumulations, as well as a deepening of color. RNA sequencing was performed to characterize the gene expression involved in ripening-related processes. A total of 1,880 non-redundant differentially expressed genes were identified by paired-comparisons between the ABA-treated and control samples at three sampling time points. The transcripts associated with starch and sucrose metabolism, flavonoid biosynthesis, and flavone and flavonol biosynthesis were significantly overrepresented. The change in the anthocyanin content following ABA treatments coincided with the expression patterns of key structural genes and an R2R2-MYB transcription factor associated with anthocyanin synthesis. Additionally, genes involved in both sucrose transportation and metabolism, such as HEXOSE TRANSPORTER and INVERTASE, had increased expression levels after ABA treatments, which was consistent with the responses of sucrose-relate enzymes. Thus, we hypothesize that ABA applications regulate many genes involved in flavonoid biosynthesis, sucrose metabolism and sugar transport that accelerate anthocyanin and hexose accumulation, thereby improving grape quality and allowing earlier harvests. These results provide extensive candidate genes involved in the ripening process under ABA treatment in grapes.