Transcriptional Control of Glutaredoxin GRXC9 Expression by a Salicylic Acid-Dependent and NPR1-Independent Pathway in Arabidopsis

Abstract

Salicylic acid (SA) is a key hormone that mediates gene transcriptional reprogramming in the context of the defense response to stress. GRXC9, coding for a CC-type glutaredoxin from Arabidopsis, is an SA-responsive gene induced early and transiently by an NPR1-independent pathway. Here, we address the mechanism involved in this SA-dependent pathway, using GRXC9 as a model gene. We first established that GRXC9 expression is induced by UVB exposure through this pathway, validating its activation in a physiological stress condition. GRXC9 promoter analyses indicate that SA controls gene transcription through two activating sequence-1 (as-1)-like elements located in its proximal region. TGA2 and TGA3, but not TGA1, are constitutively bound to this promoter region. Accordingly, the transient recruitment of RNA polymerase II to the GRXC9 promoter, as well as the transient accumulation of gene transcripts detected in SA-treated WT plants, was abolished in a knockout mutant for the TGA class II factors. We conclude that constitutive binding of TGA2 is essential for controlling GRXC9 expression, while binding of TGA3 in a lesser extent contributes to this regulation. Finally, overexpression of GRXC9 indicates that the GRXC9 protein negatively controls its own gene expression, forming part of the complex bound to the as-1-containing promoter region. These findings are integrated in a model that explains how SA controls transcription of GRXC9 in the context of the defense response to stress.Electronic supplementary materialThe online version of this article (doi:10.1007/s11105-014-0782-5) contains supplementary material, which is available to authorized users.

Plant-specific CC-type glutaredoxins: functions in developmental processes and stress responses

“…This notion is consistent with the following data set that shows that some of the CC-type GRSx function in the nucleus: first, ROXY1 cannot complement the roxy1 phenotype if it is exclusively localized in the cytosol (Li et al, 2009); secondly, MIL1 co-localizes with REC8, which is attached to meiotic chromosomes in premeiotic interphase nuclei (Hong et al, 2012); third, as mentioned above, chromatin immunoprecipitation experiments have detected ROXY19 at its own promoter (Herrera-Vásquez et al, 2014). A hallmark of the Arabidopsis ROXY-type GRXs is the CC(M/L) C or CC(M/L)S motif in the active site.…”

“…Thus, ectopically expressed ROXY19 seems to interfere with TGA2/5/6 activity at this promoter. ROXY19 also represses its own expression and direct association with its promoter was demonstrated by ChIP experiments (Herrera-Vásquez et al, 2014). ROXY19-mediated repression of ORA59 promoter activity was reconstituted in transiently transformed protoplasts.…”

Conserved redox‐dependent DNA binding of ROXY glutaredoxins with TGA transcription factors

“…This supports a function for MSCA1 interacting with the TGA TF FEA4 in reprogramming cell fates in response to altered redox conditions (Kelliher & Walbot, ). Besides these developmental ROXY/TGA functions shown by genetic studies, the combination of overexpression studies in A. thaliana together with in vitro and yeast interaction analyses supports the idea that ROXY18/19 and TGA2/5/6 function together in stress‐related processes, where redundant ROXY activities seem to hamper functional analyses (Herrera‐Vasquez et al., ; Huang et al., ; La Camera et al., ; Ndamukong et al., ; Zander et al., ).…”

“…Furthermore, the presence of the crucial MpROXY1 C‐terminal 14 amino acids is required for mediating an interaction with MpTGA and thereby also necessary for mediating the formation of a DNA‐bound complex under reducing conditions. ROXY19 from A. thaliana interacts with TGA2/5/6, but a redox‐sensitive TGA2/5/6 DNA binding has thus far not been reported as a mechanism to regulate TGA2/5/6 activities in stress responses (Herrera‐Vasquez et al., ; Zander et al., ). ROXY19 might rather affect the TGA2 activity via its interaction with TOPLESS, a transcriptional corepressor (Uhrig et al., ).…”

TGACG‐BINDING FACTORs (TGAs) and TGA‐interacting CC‐type glutaredoxins modulate hyponastic growth in Arabidopsis thaliana

“…Similarly, expression of TGA2/TGA5/TGA6‐regulating ROXY18 and ROXY19/GRX480 depends on TGA2/TGA5/TGA6 (Ndamukong et al ., ; Huang et al ., ). Endogenous ROXY18 and ROXY19/GRX480 genes are continuously repressed in 35S:ROXY19 plants (Huang et al ., ) and ROXY19/GRX480 has been detected at its own promoter by chromatin immunoprecipitation (ChIP) experiments (Herrera‐Vásquez et al ., ). This autoregulation is reminiscent of the JASMONATE‐ZIM DOMAIN ( JAZ ) repressor genes, which are activated by transcription factor MYC2 and which control their own expression by repressing MYC2 activities (Chini et al ., ).…”