Glutaredoxin family genes in plant development

ROXY1 is a gene of Arabidopsis thaliana shown to have a role in the initiation and morphogenesis of petals. ROXY1 and its homologue ROXY2 are also redundantly required for normal anther development. These genes encode plant-specific CC-type glutaredoxins (GRXs). Generally, GRXs are associated with cell redox homeostasis and the response to oxidative stress, but evidence so far shows a clear role for these genes in the coordination of development. In planta complementation work found that ROXY1 can be functionally replaced by a number of other CC-type genes of A. thaliana when expressed under the ROXY1 promoter, suggesting a shared mode of protein action. Mutagenesis analyses found a number of sites critical for function, including a conserved, but previously uncharacterised C-terminal motif. To elucidate the molecular mechanism of ROXY1 function, yeast two-hybrid experimentation was undertaken, resulting in the identification of many potential interactors including TGA and TCP transcription factors. Follow-up work found that ROXY1 has strong affinity for TGA2, TGA3, TGA7 and PERIANTHIA. Intriguingly, these interactions were dependent on the presence of the C-terminal ROXY1 motif, implying a protein binding function. Furthermore, ROXY1 was found to physically associate with a glutamine rich domain of TGA3, previously reported to be involved in transcriptional activation. Through a similar mechanism, it is likely that ROXY1 post-translationally inhibits PERIANTHIA activity in the sites of petal organogenesis, restricting AGAMOUS expression. The evolutionary history of GRX genes in the wider green lineage was also investigated. Work presented here shows that the expansion of the CC-type gene class was most rapid in the last 140 million years, as evidenced by segmental and tandem gene duplications. Gene expression profiling found that CC-type genes are expressed selectively, as opposed to other glutaredoxin gene classes exhibiting 'house-keeping' patterns of expression. Considered together, the data suggest that the CC-type-TGA association described here is an ancient mechanism sequestered to higher-plant specific roles most notably in flower development and pathogen defence, but may potentially be involved in further signalling functions.