Abstract
Global transcriptome studies demonstrated the existence of unique plant responses under combined stress which are otherwise not seen during individual stresses. In order to combat combined stress plants use signaling pathways and ‘cross talk’ mediated by hormones involved in stress and growth related processes. However, interactions among hormones’ pathways in combined stressed plants are not yet known. Here we studied dynamics of different hormones under individual and combined drought and pathogen infection in Arabidopsis thaliana by liquid chromatography-mass spectrometry (LC-MS) based profiling. Our results revealed abscisic acid (ABA) and salicylic acid (SA) as key regulators under individual drought and pathogen stress respectively. Under combined drought and host pathogen stress (DH) we observed non-induced levels of ABA with an upsurge in SA and jasmonic acid (JA) concentrations, underscoring their role in basal tolerance against host pathogen. Under a non-host pathogen interaction with drought (DNH) stressed plants, ABA, SA and JA profiles were similar to those under DH or non-host pathogen alone. We propose that plants use SA/JA dependent signaling during DH stress which antagonize ABA biosynthesis and signaling pathways during early stage of stress. The study provides insights into hormone modulation at different time points during combined stress.
Highlights
Under field conditions, drought often in combination with pathogen inflicts greater crop yield loss[1, 2]
We have studied four different scenarios of stress interactions namely drought followed by host pathogen and pathogen infection on drought stressed plants, allowing the influences of each factor to be separated, drought and non-host, and pathogen inoculation on drought recovering plants
Based on hormone and transcript profile we identified the changes in hormonal pathway under these stress interactions and compared them with similar information from individual stress experiments
Summary
Drought often in combination with pathogen inflicts greater crop yield loss[1, 2]. The SA- JA- crosstalk has been dose dependent where synergism between these two is found to be at lower endogenous concentrations which reverses to antagonism at higher concentrations of either of the two[30] In another instance, Arabidopsis thaliana quadruple mutants deficient in DELLA protein (repressors of GA-mediated responses) exhibited reduced expression of the defense gene PDF1.2 which is a marker gene of JA-mediated signaling. HopAM1 effectors modulate pathogenicity of avirulent pathogen on drought stressed plants by mediating ABA signaling[40] In an another instance ABA pretreatment lead to increased growth of the AvrXccC8004-deficient strain[41]. These arguments suggest that under natural field conditions the infection of a non-host pathogen in plants can be different during drought stress. Based on microarray data, we correlate the hormone content at early time point at 8 h and late time point at 24 h post treatments in regulating the derived signaling or hormone biosynthesis respectively
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