A G-protein β subunit, AGB1, negatively regulates the ABA response and drought tolerance by down-regulating AtMPK6-related pathway in Arabidopsis.

Dong-Bei Xu,Yao-Feng Chen,Ya-Nan Ma,Zhao-Shi Xu,Lian-Cheng Li,You-Zhi Ma,Ming Chen,Hong Zhang

doi:10.1371/journal.pone.0116385

Abstract

Heterotrimeric G-proteins are versatile regulators involved in diverse cellular processes in eukaryotes. In plants, the function of G-proteins is primarily associated with ABA signaling. However, the downstream effectors and the molecular mechanisms in the ABA pathway remain largely unknown. In this study, an AGB1 mutant (agb1-2) was found to show enhanced drought tolerance, indicating that AGB1 might negatively regulate drought tolerance in Arabidopsis. Data showed that AGB1 interacted with protein kinase AtMPK6 that was previously shown to phosphorylate AtVIP1, a transcription factor responding to ABA signaling. Our study found that transcript levels of three ABA responsive genes, AtMPK6, AtVIP1 and AtMYB44 (downstream gene of AtVIP1), were significantly up-regulated in agb1-2 lines after ABA or drought treatments. Other ABA-responsive and drought-inducible genes, such as RD29A (downstream gene of AtMYB44), were also up-regulated in agb1-2 lines. Furthermore, overexpression of AtVIP1 resulted in hypersensitivity to ABA at seed germination and seedling stages, and significantly enhanced drought tolerance in transgenic plants. These results suggest that AGB1 was involved in the ABA signaling pathway and drought tolerance in Arabidopsis through down-regulating the AtMPK6, AtVIP1 and AtMYB44 cascade.

Highlights

Heterotrimeric GTP-binding proteins (G-proteins) are evolutionarily conserved plasma membrane-bound proteins that regulate a number of fundamental processes in eukaryotic organisms
Our results demonstrated that AGB1 interacts with AtMPK6 and may negatively regulate the ABA signaling pathway and drought tolerance by down-regulating the AtMPK6, AtVIP1, and AtMYB44 cascade in Arabidopsis
Transcripts of AtMPK6 in agb1-2 lines were significantly increased at 0.5 h and 1 h after ABA treatment compared to those in WT (S4 Fig.). These results indicated that AGB1 might negatively regulate the ABA signaling pathway in Arabidopsis by down-regulating expression of AtMPK6, AtVIP1 and AtMYB44 under ABA or drought treatments

Summary

Introduction

Heterotrimeric GTP-binding proteins (G-proteins) are evolutionarily conserved plasma membrane-bound proteins that regulate a number of fundamental processes in eukaryotic organisms. A G-Protein β Subunit in ABA Signaling and Drought Tolerance and three Gγ (AGG1-AGG3) genes [4,5]. Loss-of-function mutants and gain-of-function lines overexpressing G-protein subunits and signaling components showed that G-proteins play a vital role in regulating diverse growth and developmental processes, hormonal and stress responses [6,7]. AGB1 functions in many facets of development and signal transduction in Arabidopsis, for example, agb mutants display diverse phenotypes with highly branched root systems, rounder leaves as well as shorter siliques [8], and have altered sensitivity to brassinosteroid (BR) and ABA during seed germination, and altered sugar sensing and stomate closure [9,10,11,12,13]

Methods

Results

Discussion

Conclusion