Quantitative Proteomics-Based Analysis Supports a Major Role Of GTG Proteins In Regulation Of ABA Response In Arabidopsis Roots

Abscisic acid (ABA) is perceived by multiple receptors, both soluble and plasma membrane-localized. We have previously reported on the role of two GPCR-type G-proteins (GTG proteins) as plasma membrane-localized ABA receptors; however, due to the presence of multiple transmembrane domains, a detailed structure-function characterization of GTG proteins remains limited. Since ABA induces massive changes in the proteome of plants, a labeling LC-based quantitative proteomics approach using iTRAQ was applied to the wild-type and gtg1gtg2 mutant Arabidopsis thaliana roots to elucidate the global effects and possible downstream targets of GTG proteins. Quantitative differences in protein abundance were analyzed for evaluation of the effect of ABA on the root proteome and its dependence on the presence of functional GTG1/GTG2 receptors. The results reported in this study reveal the most elaborate ABA-responsive root proteome identified to date in Arabidopsis. Notably, the majority of ABA-responsive proteins required the presence of GTG proteins, supporting their key role in ABA perception. Comparative analysis of the ABA-dependent protein abundance changes in the WT versus gtg1gtg2 mutants provides clues to the downstream signaling pathways of the GTG receptors that are compromised in gtg1gtg2 plants and their possible link to some of the well-established effectors of the ABA signaling pathways.