The Mg-Chelatase H Subunit ofArabidopsisAntagonizes a Group of WRKY Transcription Repressors to Relieve ABA-Responsive Genes of Inhibition  

Abstract

The phytohormone abscisic acid (ABA) plays a vital role in plant development and response to environmental challenges, but the complex networks of ABA signaling pathways are poorly understood. We previously reported that a chloroplast protein, the magnesium-protoporphyrin IX chelatase H subunit (CHLH/ABAR), functions as a receptor for ABA in Arabidopsis thaliana. Here, we report that ABAR spans the chloroplast envelope and that the cytosolic C terminus of ABAR interacts with a group of WRKY transcription factors (WRKY40, WRKY18, and WRKY60) that function as negative regulators of ABA signaling in seed germination and postgermination growth. WRKY40, a central negative regulator, inhibits expression of ABA-responsive genes, such as ABI5. In response to a high level of ABA signal that recruits WRKY40 from the nucleus to the cytosol and promotes ABAR-WRKY40 interaction, ABAR relieves the ABI5 gene of inhibition by repressing WRKY40 expression. These findings describe a unique ABA signaling pathway from the early signaling events to downstream gene expression.

The rice transcription factor OsWRKY47 is a positive regulator of the response to water deficit stress

“…Binding preferences of WRKY TFs have not been deeply explored so far. However, some interesting examples are available in the literature; AtWRKY18 which is involved in ABA signaling and salt tolerance (Chen et al 2010;Shang et al 2010) binds the sequence (C/A)TTGAC(T/G). AtWRKY6, a negative regulator of the response to low Pi levels and a positive regulator to low brassinosteroid levels (Chen et al 2009;Kasajima et al 2010), binds specifically the sequence GTTGACC, a sequence similar to that bound by OsWRKY47 (Ciolkowski et al 2008).…”

A systems biology perspective on the role of WRKY transcription factors in drought responses in plants

“…A detailed analysis of the abo3 mutant illustrates some of the roles of this wRKY transcription factor by placing AtwRKY63 downstream of ABI1, ABI2 and ABI5 but upstream of ABF2, RD29A and COR4. Interestingly, AtwRKY40 appears to act upstream of the bZIP transcription factor ABI5 (Shang et al 2010) whereas AtwRKY63 acts downstream of it and hence taken together, this shows that there is a cascade of transcription factors initiated by ABA with AtwRKY40 repressing ABI5 gene expression in the absence of ABA. Upon ABA perception, derepression of ABI5 leads to activation of AtWRKY63 at Shekhawat et al (2011) the transcriptional level which further activates the target genes including RD29A and COR47 (Rushton et al 2012).…”

“…There are many other examples of wRKY-MAP kinase interactions (Chi et al 2013). Other interacting partners of wRKY proteins include 14-3-3 proteins (Chang et al 2009), chromatin remodeling proteins such as Arabidopsis histone deacetylase 19 (Kim et al 2010), vQ proteins ), CC-NBR-LRR-type R proteins (Shen et al 2007), e3 ubiquitin ligases (Miao and Zentgraf 2010) and the chloroplast ⁄ plastid-localized ABA receptor, ABAR (Shang et al 2010). These interacting partners of wRKY TFs are providing increasing information as to the roles and mechanisms involved in wRKY TF action at the systems level.…”

The Potential of Transcription Factor-Based Genetic Engineering in Improving Crop Tolerance to Drought

“…Techniques such as yeast two-hybrid screens and affinity purification mass spectrophotometry (AP-MS) can be utilized to find interacting protein partners. Yeast two-hybrid (Y2H) assays (Fields and Song, 1989) are a popular tool and Shang et al (2010) used this approach to show the interaction between an ABA receptor (ABAR) and AtWRKY40 using the ABAR C-terminus as the bait. BiFC is a noninvasive fluorescent-based technique that allows visualization of protein-protein interactions in living cells and is most commonly used to investigate known interactions between two proteins (Ohad et al, 2007).…”