AtWRKY40 and AtWRKY63 Modulate the Expression of Stress-Responsive Nuclear Genes Encoding Mitochondrial and Chloroplast Proteins    

Abstract

The expression of a variety of nuclear genes encoding mitochondrial proteins is known to adapt to changes in environmental conditions and retrograde signaling. The presence of putative WRKY transcription factor binding sites (W-boxes) in the promoters of many of these genes prompted a screen of 72 annotated WRKY factors in the Arabidopsis (Arabidopsis thaliana) genome for regulators of transcripts encoding mitochondrial proteins. A large-scale yeast one-hybrid screen was used to identify WRKY factors that bind the promoters of marker genes (Alternative oxidase1a, NADH dehydrogenaseB2, and the AAA ATPase Ubiquinol-cytochrome c reductase synthesis1), and interactions were confirmed using electromobility shift assays. Transgenic overexpression and knockout lines for 12 binding WRKY factors were generated and tested for altered expression of the marker genes during normal and stress conditions. AtWRKY40 was found to be a repressor of antimycin A-induced mitochondrial retrograde expression and high-light-induced signaling, while AtWRKY63 was identified as an activator. Genome-wide expression analysis following high-light stress in transgenic lines with perturbed AtWRKY40 and AtWRKY63 function revealed that these factors are involved in regulating stress-responsive genes encoding mitochondrial and chloroplast proteins but have little effect on more constitutively expressed genes encoding organellar proteins. Furthermore, it appears that AtWRKY40 and AtWRKY63 are particularly involved in regulating the expression of genes responding commonly to both mitochondrial and chloroplast dysfunction but not of genes responding to either mitochondrial or chloroplast perturbation. In conclusion, this study establishes the role of WRKY transcription factors in the coordination of stress-responsive genes encoding mitochondrial and chloroplast proteins.

Arabidopsis MYC Transcription Factors Are the Target of Hormonal Salicylic Acid/Jasmonic Acid Cross Talk in Response to Pieris brassicae Egg Extract

“…Since several WRKYs have been reported to modulate SA/JA antagonism (Caarls et al, 2015), this prompted us to test the involvement of this factor in response to egg extract treatment. The Arabidopsis T-DNA insertion mutant wrky75-25 (Encinas-Villarejo et al, 2009) and a 35S:WRKY75 overexpressor line (Van Aken et al, 2013) were treated with P. brassicae egg extract and subsequently wounded. Controls consisted of no treatment or wounding alone.…”

The Membrane-Bound NAC Transcription Factor ANAC013 Functions in Mitochondrial Retrograde Regulation of the Oxidative Stress Response in Arabidopsis

“…ABSCISIC ACID INSENSITIVE4 (ABI4) represses the basal expression of the Arabidopsis AOX1a gene, thereby allowing derepression by MRR , and is also a common component of multiple chloroplast RTG pathways (Koussevitzky et al, 2007). In addition, CYCLIN-DEPENDENT KINASE E;1 and WRKY40 have been identified as positive and negative regulators of MRR induction of AOX1a in Arabidopsis, respectively (Ng et al, 2013a;Van Aken et al, 2013). Although the effect of mitochondrial dysfunction on nuclear gene expression has been elucidated (Schwarzländer et al, 2012), the current understanding of the underlying regulatory mechanisms in plants is still limited.…”

A Membrane-Bound NAC Transcription Factor, ANAC017, Mediates Mitochondrial Retrograde Signaling in Arabidopsis

“…However, the identities of these mrrd mutants are yet to be characterized. To date, three components mediating the mitochondrial retrograde response in plants have been identified: ABSCISIC ACID INSENSITIVE4 (ABI4) ), CYCLIN-DEPENDENT KINASE E;1 (Ng et al, 2013), and WRKY40 (Van Aken et al, 2013).In this work, we employed a forward genetic approach using AOX1a as marker gene for mitochondrial retrograde regulation to identify regulators of aox1a (rao) mutants. Here, we report a membrane-bound NAC (for NO APICAL MERISTEM/ARABI-DOPSIS TRANSCRIPTION ACTIVATION FACTOR/CUP-SHAPED COTYLEDON) transcription factor, RAO2/Arabidopsis NAC domain-containing protein17 (ANAC017), that is a transcriptional activator of AOX1a during mitochondrial dysfunction.…”