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First published online February 13, 2009; 10.1105/tpc.109.210210

The Plant Cell 21:363

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IN BRIEF

Glutaredoxin Functions in Floral Development

Nancy R. Hofmann

Science Editor

nhofmann{at}aspb.org

Glutaredoxins (GRXs) are glutathione-dependent disulfide oxidoreductases that are well documented to be involved in oxidative stress responses in plants (reviewed in Rouhier et al., 2008Go). GRXs allow for redox regulation of protein activity by reversibly glutathionylating or reducing disulfide bridges in their targets. Intriguingly, ROXY1 and ROXY2, two members of a land plant-specific class of GRXs, recently have been found to be required for petal development in Arabidopsis thaliana (Xing et al., 2005Go; Xing and Zachgo, 2008Go). Current work from Li et al. (pages 429–441) finds that this likely occurs via posttranslational modification of transcription factors.

Li et al. began by establishing that ROXY1 acts in the nucleus by correlating the localizations of ROXY1 fusion proteins with their abilities to complement the roxy1 mutant. These experiments showed that nuclear localization of ROXY1 is necessary and sufficient for ROXY1 function (see figure ). Consistent with a role in the nucleus, both yeast two-hybrid and bimolecular fluorescence complementation assays demonstrated that ROXY1 interacts with several TGA transcription factors, including TGA2, TGA3, TGA7, and PERIANTHIA (PAN). This interaction with PAN is especially interesting because PAN is known to be involved in regulating floral organ primordium formation.


Figure 1
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  		Nuclear localization is required for ROXY1 function. ROXY1 fused to three copies of yellow fluorescent protein (3xYFP) localizes to the cytoplasm (top, left panel) unless a nuclear localization signal (NLS) is present (top, right panel). The roxy1 phenotype is rescued only when the NLS is present (bottom panels). (Adapted from Figure 1 in Li et al. [2009]Go.)

 
In situ hybridizations showed that ROXY1 expression patterns overlap with those of TGA2 and PAN in developing floral tissues, supporting the physiological relevance of the molecular interactions described above. Since PAN is involved in floral development, the authors examined the genetic interactions between ROXY1 and PAN. While the pan single mutant forms flowers with increased floral organ numbers, the roxy1 single mutant has flowers with fewer petals and later petal morphogenesis defects. The roxy1 pan double mutant had extra floral organs. Thus, PAN is epistatic to ROXY1, which is consistent with PAN being a target of ROXY1 in the regulation of petal primordium initiation. The double mutant also had later petal defects, indicating that ROXY1 functions independently of PAN later in petal development. Indeed, when the authors generated a transgenic line in which the expression of target genes of PAN and related TGA transcription factors was dominantly repressed, it had more defective floral phenotypes than could be explained by the lack of PAN alone. This suggests that other TGA transcription factors are involved in flower development.

Since ROXY1 is a GRX and likely acts on its targets via modification of a Cys residue, Li et al. checked the effects of mutagenizing PAN's six Cys residues individually. Mutating a Cys residue found in a conserved region of PAN thought to be a transactivating domain eliminated the protein's ability to rescue the pan mutant. Thus, this Cys might be a target for ROXY1 regulation of PAN activity. Together, the results of Li et al. point to a new mechanism for regulation of floral development, in which redox-sensitive TGA transcription factors are likely posttranslationally modified by members of a plant-specific class of GRXs.

Footnotes

www.plantcell.org/cgi/doi/10.1105/tpc.109.210210

REFERENCES

Li, S., Lauri, A., Ziemann, M., Busch, A., Bhave, M., and Zachgo, S. (2009). Nuclear activity of ROXY1, a glutaredoxin interacting with TGA factors, is required for petal development in Arabidopsis thaliana. Plant Cell 21: 429–441.[Abstract/Free Full Text]

Rouhier, N., Lemaire, S.D., and Jacquot, J.-P. (2008). The role of glutathione in photosynthetic organisms: Emerging functions for glutaredoxins and glutathionylation. Annu. Rev. Plant Biol. 59: 143–166.[CrossRef][Medline]

Xing, S., Rosso, M.G., and Zachgo, S. (2005). ROXY1, a member of the plant glutaredoxin family, is required for petal development in Arabidopsis thaliana. Development 132: 1555–1565.[Abstract/Free Full Text]

Xing, S., and Zachgo, S. (2008). ROXY1 and ROXY2, two Arabidopsis glutaredoxin genes, are required for anther development. Plant J. 53: 790–801.[CrossRef][Web of Science][Medline]


Related articles in Plant Cell:

Nuclear Activity of ROXY1, a Glutaredoxin Interacting with TGA Factors, Is Required for Petal Development in Arabidopsis thaliana
Shutian Li, Andrea Lauri, Mark Ziemann, Andrea Busch, Mrinal Bhave, and Sabine Zachgo
Plant Cell 2009 21: 429-441. [Abstract] [Full Text]  




This Article
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