Molecular and physiological analysis of drought stress in Arabidopsis reveals early responses leading to acclimation in plant growth.

Amal Harb,Arjun Krishnan,Madana M R Ambavaram,Andy Pereira

doi:10.1104/pp.110.161752

Abstract

Plant drought stress response and resistance are complex biological processes that need to be analyzed at a systems level using genomics and physiological approaches to dissect experimental models that address drought stresses encountered by crops in the field. Toward this goal, a controlled, sublethal, moderate drought (mDr) treatment system was developed in Arabidopsis (Arabidopsis thaliana) as a reproducible assay for the dissection of plant responses to drought. The drought assay was validated using Arabidopsis mutants in abscisic acid (ABA) biosynthesis and signaling displaying drought sensitivity and in jasmonate response mutants showing drought resistance, indicating the crucial role of ABA and jasmonate signaling in drought response and acclimation. A comparative transcriptome analysis of soil water deficit drought stress treatments revealed the similarity of early-stage mDr to progressive drought, identifying common and specific stress-responsive genes and their promoter cis-regulatory elements. The dissection of mDr stress responses using a time-course analysis of biochemical, physiological, and molecular processes revealed early accumulation of ABA and induction of associated signaling genes, coinciding with a decrease in stomatal conductance as an early avoidance response to drought stress. This is accompanied by a peak in the expression of expansin genes involved in cell wall expansion, as a preparatory step toward drought acclimation by the adjustment of the cell wall. The time-course analysis of mDr provides a model with three stages of plant responses: an early priming and preconditioning stage, followed by an intermediate stage preparatory for acclimation, and a late stage of new homeostasis with reduced growth.

Highlights

Plant drought stress response and resistance are complex biological processes that need to be analyzed at a systems level using genomics and physiological approaches to dissect experimental models that address drought stresses encountered by crops in the field
Most of the key genes in these pathways have been identified, such as transcription factors belonging to the class of DRE-binding protein (DREB)/ C-repeat-binding factor (CBF), abscisic acid (ABA)-binding factor (ABF), MYC, and MYB (Abe et al, 1997; Bartels and Sunkar, 2005; Sakuma et al, 2006), including the identification of the stress-responsive cis-elements ABA-responsive element (ABRE) and dehydrationresponsive element (DRE; Yamaguchi-Shinozaki and Shinozaki, 1994; Ramanjulu and Bartels, 2002; Bartels and Sunkar, 2005)
Plants were grown under well-watered conditions, and drought stress was applied by withholding water at different growth stages to three batches of plants: at 25 d after sowing (DAS), 30 DAS, and 35 DAS

Summary

Introduction

The dissection of mDr stress responses using a time-course analysis of biochemical, physiological, and molecular processes revealed early accumulation of ABA and induction of associated signaling genes, coinciding with a decrease in stomatal conductance as an early avoidance response to drought stress. Downstream of the early signal perception events, signaling genes and molecules acting as secondary messengers have been identified, revealing the role of Ca+ and reactive oxygen species (ROS) as secondary messengers (Bartels and Sunkar, 2005) These regulatory mechanisms induce downstream functional genes, which are needed to establish new cellular homeostasis that leads to drought tolerance and/or resistance (Yancey, 2001; Ramanjulu and Bartels, 2002)

Methods

Results

Conclusion