Abstract
BackgroundSuppression and activation of plant defense genes is comprehensively regulated by WRKY family transcription factors. Chickpea, the non-model crop legume suffers from wilt caused by Fusarium oxysporum f. sp. ciceri Race1 (Foc1), defense response mechanisms of which are poorly understood. Here, we attempted to show interaction between WRKY70 and several downstream signaling components involved in susceptibility/resistance response in chickpea upon challenge with Foc1.ResultsIn the present study, we found Cicer arietinum L. WRKY70 (CaWRKY70) negatively governs multiple defense responsive pathways, including Systemic Acquired Resistance (SAR) activation in chickpea upon Foc1 infection. CaWRKY70 is found to be significantly accumulated at shoot tissues of susceptible (JG62) chickpea under Foc1 stress and salicylic acid (SA) application. CaWRKY70 overexpression promotes susceptibility in resistant chickpea (WR315) plants to Foc1 infection. Transgenic plants upon Foc1 inoculation demonstrated suppression of not only endogenous SA concentrations but expression of genes involved in SA signaling. CaWRKY70 overexpressing chickpea roots exhibited higher ion-leakage and Foc1 biomass accumulation compared to control transgenic (VC) plants. CaWRKY70 overexpression suppresses H2O2 production and resultant reactive oxygen species (ROS) induced cell death in Foc1 infected chickpea roots, stem and leaves. Being the nuclear targeted protein, CaWRKY70 suppresses CaMPK9-CaWRKY40 signaling in chickpea through its direct and indirect negative regulatory activities. Protein-protein interaction study revealed CaWRKY70 and CaRPP2-like CC-NB-ARC-LRR protein suppresses hyper-immune signaling in chickpea. Together, our study provides novel insights into mechanisms of suppression of the multiple defense signaling components in chickpea by CaWRKY70 under Foc1 stress.ConclusionCaWRKY70 mediated defense suppression unveils networking between several immune signaling events negatively affecting downstream resistance mechanisms in chickpea under Foc1 stress.
Highlights
Suppression and activation of plant defense genes is comprehensively regulated by WRKY family transcription factors
WRKY70 (CaWRKY70) under salicylic acid (SA) induction and Foc1 infection CaWRKY70 expression in different chickpea tissues were determined by quantitative real-time Polymerase chain reaction (PCR) analysis
Results demonstrate that CaWRKY64 and CaWRKY70 tagged to C-terminus of yellow fluorescence protein (YFP) interact with fulllength Coiled coil (CC)-Nucleotide binding oligomerization domain leucine rich repeat (NLR) protein fused to N-terminus of YFP
Summary
Suppression and activation of plant defense genes is comprehensively regulated by WRKY family transcription factors. Plant defense against pathogens are rapidly conveyed through cell surface receptors or by the intracellular immune receptors. Cell surface receptors usually recognize specific pathogen or microbe associated molecular patterns (i.e., PAMPs or MAMPs) and elicits Pattern Triggered Immunity (PTI). Intracellular receptors bind PTI suppressing effector proteins released by the pathogens which induce strong immune response, known as Effector Triggered Immunity (ETI) [1, 2]. WRKY transcription factors (TFs) are indispensable regulators of both PTI and ETI to wide variety of pathogens. The members of large multigene family transcription factor comprise WRKY domain (WRKYGQK) and zinc finger motif (CX47CX22-23HXH/C) that binds at TGAC core of W-box containing DNA [3, 4]. There are 74 WRKY family members present in Arabidopsis thaliana, which have been classified into three major groups (I, II and III) based on the number and position of WRKY domains and features of the zinc finger motif [5]
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