SA‐inducible Arabidopsis glutaredoxin interacts with TGA factors and suppresses JA‐responsive PDF1.2 transcription

Abstract

SummarySalicylic acid (SA) is a plant signaling molecule that mediates the induction of defense responses upon attack by a variety of pathogens. Moreover, it antagonizes gene induction by the stress signaling molecule jasmonic acid (JA). Several SA-responsive genes are regulated by basic/leucine zipper-type transcription factors of the TGA family. TGA factors interact with NPR1, a central regulator of many SA-induced defense responses including SA/JA antagonism. In order to identify further regulatory proteins of SA-dependent signaling pathways, a yeast protein interaction screen with tobacco TGA2.2 as bait and an Arabidopsis thaliana cDNA prey library was performed and led to the identification of a member of the glutaredoxin family (GRX480, encoded by At1g28480). Glutaredoxins are candidates for mediating redox regulation of proteins because of their capacity to catalyze disulfide transitions. This agrees with previous findings that the redox state of both TGA1 and NPR1 changes under inducing conditions. Transgenic Arabidopsis plants ectopically expressing GRX480 show near wild-type expression of standard marker genes for SA-and xenobiotic-inducible responses. In contrast, transcription of the JA-dependent defensin gene PDF1.2 was antagonized by transgenic GRX480. This, together with the observation that GRX480 transcription is SA-inducible and requires NPR1, suggests a role of GRX480 in SA/JA cross-talk. Suppression of PDF1.2 by GRX480 depends on the presence of TGA factors, indicating that the GRX480/TGA interaction is effective in planta.

The ROXY1 C-Terminal L**LL Motif Is Essential for the Interaction with TGA Transcription Factors

“…ROXY4 is a target gene up-regulated by DELLA and participates in GA signaling and floral organ development (Hou et al, 2008). ROXY19 is known to function in pathogen defense (Ndamukong et al, 2007). The capability of this subclass of ROXYs to exhibit ROXY1-like activities in flower development depends on the presence of an L**LL motif in their a5 helix.…”

“…ROXY1 and its closest homolog ROXY2 act redundantly during anther development and microspore formation (Xing and Zachgo, 2008). The other two CC-type GRX genes with known functions, ROXY19 (originally named GRX480) and ROXY4, participate in pathogen defense responses and GA signaling in Arabidopsis, respectively (Ndamukong et al, 2007;Hou et al, 2008).…”

“…TGA transcription factors have been recently identified as interaction proteins of ROXYs and thus are likely posttranslationally modified by ROXYs (Ndamukong et al, 2007;. TGA transcription factors belong to the basic leucine zipper (bZIP) protein superfamily and comprise 10 members in Arabidopsis: TGA1 to TGA7, PERIANTHIA (PAN), TGA9, and TGA10 (Jakoby et al, 2002;Murmu et al, 2010).…”

“…Genetic analysis and protein interaction experiments indicate that the CC-type GRXs might modify TGA transcription factors by catalyzing thiol-disulfide exchange or deglutathionylation reactions through conserved Cys residues, thereby regulating their activity and related biological processes Ndamukong et al, 2007;Murmu et al, 2010). Upon pathogen infection and salicylic acid accumulation, NONEXPRESSOR OF PR GENES1 (NPR1) is translocated from the cytoplasm into the nucleus and interacts with TGA transcription factors.…”

“…The NPR1/TGA1 protein interaction depends on the reduced state of two Cys residues in TGA1, as an intramolecular disulfide bridge formed between Cys-260 and Cys-266 prevents this interaction (Després et al, 2003). Salicylic acid-induced ROXY19 interacts with several TGA transcription factors and negatively modulates jasmonic acid-responsive PDF1.2 transcription in Arabidopsis, suggesting that this GRX is involved in the reduction of TGA1 (Ndamukong et al, 2007). The floral CC-type GRX ROXY1 protein interacts with PAN in the nucleus, which was shown to be a prerequisite to exert proper functions during floral organ development .…”