Analysis of the function of plant specific CCMC-type glutaredoxins that interact with the bZIP transcription factors of the TGA family

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The elucidation of plant defense strategies against pathogens constitutes an important area of research. In the course of the defense reaction, the intracellular redox state changes dramatically and redox control of important regulatory proteins have been described. Glutaredoxins (GRXs) are small proteins of approximately 12 kDa that are able to catalyze the reduction of intra- or intermolecular disulfide bridges or glutathione (GSH) mixed disulfides. The Arabidopsis genome encodes 30 GRX genes that have been classified into three major groups according to the amino acid sequence in their redox active center. All the seven glutaredoxins that are characterized by a CCMC motif interact with the bZIP transcription factors of the TGA family which are important signalling components of the salicylic acid (SA)- inducible plant defense response “systemic acquired resistance (SAR)”. A functional role for these TGA-interacting glutaredoxins in plant defense responses seems likely, as a subgroup of TGA transcription factors is subject to redox changes when plants are treated with SA. In addition, critical cysteines of NPR1, an ankyrin repeat protein that interacts with TGA factors and that is indispensable for SAR establishment, are reduced under inducing conditions. Expression of three of the TGA-interacting glutaredoxins is SA-inducible. We have recently shown that a GRX/TGA complex is involved the negative cross-talk between SA and jasmonic acid. The aim of the project is to elucidate the function of the SA-inducible, TGAinteracting members of the glutaredoxin family. We will address an important regulatory principle in plant defense responses that involves the poorly understood mechanisms of redox modifications of regulatory proteins.