TheArabidopsisGRAS Protein SCL14 Interacts with Class II TGA Transcription Factors and Is Essential for the Activation of Stress-Inducible Promoters

Abstract

The plant signaling molecule salicylic acid (SA) and/or xenobiotic chemicals like the auxin mimic 2,4-D induce transcriptional activation of defense-and stress-related genes that contain activation sequence-1 (as-1)-like cis-elements in their promoters. as-1-like sequences are recognized by basic/leucine zipper transcription factors of the TGA family. Expression of genes related to the SA-dependent defense program systemic acquired resistance requires the TGA-interacting protein NPR1. However, a number of as-1-containing promoters can be activated independently from NPR1. Here, we report the identification of Arabidopsis thaliana SCARECROW-like 14 (SCL14), a member of the GRAS family of regulatory proteins, as a TGA-interacting protein that is required for the activation of TGA-dependent but NPR1-independent SA-and 2,4-Dinducible promoters. Chromatin immunoprecipitation experiments revealed that class II TGA factors TGA2, TGA5, and/or TGA6 are needed to recruit SCL14 to promoters of selected SCL14 target genes identified by whole-genome transcript profiling experiments. The coding regions and the expression profiles of the SCL14-dependent genes imply that they might be involved in the detoxification of xenobiotics and possibly endogenous harmful metabolites. Consistently, plants ectopically expressing SCL14 showed increased tolerance to toxic doses of the chemicals isonicotinic acid and 2,4,6-triiodobenzoic acid, whereas the scl14 and the tga2 tga5 tga6 mutants were more susceptible. Hence, the TGA/SCL14 complex seems to be involved in the activation of a general broad-spectrum detoxification network upon challenge of plants with xenobiotics.

Molecular mechanisms of desiccation tolerance in the resurrection glacial relic Haberlea rhodopensis

“…Some of them could act as master switches of growth, development, and stress-related genetic programs. For example, members of the GRAS family of transcription factors regulate many developmental processes and stress responses in A. thaliana, including salt and drought tolerance [50,51]. MADSbox transcription factors are better known for their involvement in developmental processes and floral organ identity formation but in Haberlea the drought-induced MADS-box transcription factor may be unique to this species or have functions distinct from those of their homologues in other species.…”

Safeners recruit multiple signalling pathways for the orchestrated induction of the cellular xenobiotic detoxification machinery in Arabidopsis

“…During the induction of SAR, a late response to SA, TGA factors interact with NPR1 and activate transcription via the cognate TGA boxes (TGACG) in the promoters of PR genes (Rochon et al 2006). The early response to SA and other chemical stresses, on the other hand, is mediated by TGA factors interacting with SCL14, a member of the GRAS family regulatory proteins, through as-1 (TGACGTCAnnnnTGACGTCA) promotor elements (Fode et al 2008). Consistently, as-1 elements were found to be overrepresented in the cluster of 31 immediate-early SA response genes activated by TGA factors in an NPR1-independent manner (Blanco et al 2009).…”

“…Class II TGA transcription factors are thus involved in the activation of multiple stress responses. They mediate the induction of PR gene expression and SAR in response to biotrophic pathogens (Zhang et al 2003), and they are involved in the activation of detoxification responses after exposure to chemical stresses (Fode et al 2008;Mueller et al 2008). Furthermore, class II TGA factors were recently shown to modulate the ethylene and jasmonic acid-dependent responses to necrotrophic pathogens (Zander et al 2009).…”

The Single-Stranded DNA-Binding Protein WHIRLY1 Represses WRKY53 Expression and Delays Leaf Senescence in a Developmental Stage-Dependent Manner in Arabidopsis

“…Using real-time PCR, the enrichment of the immunoprecipitated DNAs was determined. Data analysis was adapted to published work (Fode et al, 2008), where the amplicon level in the why1 mutant was calibrated to 1 and the relative fold enrichment in the PWHY1-HA line was calculated upon the why1 mutant. For estimation of the percentage input, a standard curve using the following dilutions of the input DNA (DNA from chromatin without immunoprecipitation) was generated for each amplicon: 0.12%, 0.06%, 0.03%, 0.015%, 0.0075%, and 0.00375%.…”