ABA Signaling in Grapevine

Abscisic acid (ABA) regulates various developmental processes and stress responses over both short (i.e. hours or days) and longer (i.e. months or seasons) time frames. In order to understand the transcriptional regulatory network of grapevine (Vitis vinifera) responding to ABA in a short-term response, different organs of grape (berries, shoot tips, leaves, roots and cell cultures) were treated with 10 μM (S)-(+)-ABA for 2 h. Nimblegen whole genome microarrays for genes of Vitis viniferawere used to determine the effects of ABA on organ-specific mRNA expression patterns.

Results of transcriptomic analysis revealed 642 genes whose mRNA abundances varied significantly in different organs in response to ABA treatment.  It demonstrated that only one gene exhibited the same organ-specific changes across all organs. The biochemical pathways affected by ABA were analyzed using the Cytoscape program with the Bingo plug-in software. The results indicated that these genes were involved in several biological processes such as response to ABA, response to reactive oxygen species, and response to water deficit. ABA affected mRNA abundance of genes associated with ABA degradation, conjugation, and the ABA signaling pathway (CYP707As, UGT73B1, and PP2Cs). There were several transcription factors that were significantly affected by ABA (e.g. AP2/ERF, MYC/MYB, and bZIP/AREB). Each organ had unique gene expression responses to ABA. The greatest number of differentially expressed genes due to the treatment effect was observed in the roots followed by cell cultures, leaves, berries, and shoot tips, respectively. In berries, differentially expressed genes were mainly involved in metabolic process while in shoots they were mainly involved in response to water deficit. Biological processes of over-represented genes in leaves were responsible for leaf morphogenesis. Responses of the roots and cell culture to ABA had the most overlap in gene expression and biological processes, which were mainly involved in phosphorylation and degradation.

This study elucidated the effects of ABA on different organs of grapevine. The responses of each organ were unique to ABA indicating that ABA signaling varies with the organ. Understanding the ABA responses in an organ-specific manner is crucial to fully understand hormone action and plant responses to osmotic stress.