Plant-Specific Glutaredoxins

To gain insight in how clade II TGA factors mediate different responses, we isolated interacting proteins using a protein interaction screen in yeast. This screen yielded the glutaredoxin ROXY19 and the GRAS protein SCL14.

Glutaredoxins catalyze the reduction of glutathionylated cysteine residues and disulfide bridges by transferring electrons from glutathione (GSH) to oxidized cysteine residues of target proteins. Moreover, they are involved in the synthesis and assembly of iron/sulphur clusters and the synthesis of deoxyribonucleotides.

Based on the amino acid sequence of the active site, glutaredoxins are divided into three classes, namely the CPYC, CGFS, and CC-type (ROXY) class. CPYC and CGFS-type glutaredoxins are found in all organisms including plant species.

The CC-type (ROXY) occurs only in land plants where the corresponding genes have undergone several rounds of gene duplication yielding 21 genes in Arabidopsis (Ziemann et al., 2009). Mutation of ROXY1 results in a developmental phenotype with reduced numbers of petals (Xing et al., 2005). This finding already indicates that CC-type glutaredoxins are involved in plant-specific processes.

Whereas ROXY1 and ROXY2 are involved in flower development, ROXY19/GRX480 has been shown to negatively regulate the defense pathway that is activated by the plant hormones jasmonic acid (JA) and ethylene (ET) (Ndamukong et al., 2007). In both functional contexts, ROXYs physically and genetically interact with the TGA bZIP transcription factors.

• Redox-modification of TGA factors and TGA-interacting proteins by glutaredoxins ROXY18, ROXY19 and ROXY9.