The effects of redox controls mediated by glutathione peroxidases on root architecture in Arabidopsis thaliana

Glutathione peroxidases (GPXs) fulfil important functions in oxidative signalling and protect against the adverse effects of excessive oxidation. However, there has been no systematic characterization of the functions of the different GPX isoforms in plants. The roles of the different members of the Arabidopsis thaliana GPX gene (AtGPX) family were therefore investigated using gpx1, gpx2, gpx3, gpx4, gpx6, gpx7, and gpx8 T-DNA insertion mutant lines. The shoot phenotypes were largely similar in all genotypes, with small differences from the wild type observed only in the gpx2, gpx3, gpx7, and gpx8 mutants. In contrast, all the mutants showed altered root phenotypes compared with the wild type. The gpx1, gpx4, gpx6, gpx7, and gpx8 mutants had a significantly greater lateral root density (LRD) than the wild type. Conversely, the gpx2 and gpx3 mutants had significantly lower LRD values than the wild type. Auxin increased the LRD in all genotypes, but the effect of auxin was significantly greater in the gpx1, gpx4, and gpx7 mutants than in the wild type. The application of auxin increased GPX4 and GPX7 transcripts, but not GPX1 mRNAs in the roots of wild-type plants. The synthetic strigolactone GR24 and abscisic acid (ABA) decreased LRD to a similar extent in all genotypes, except gpx6, which showed increased sensitivity to ABA. These data not only demonstrate the importance of redox controls mediated by AtGPXs in the control of root architecture but they also show that the plastid-localized GPX1 and GPX7 isoforms are required for the hormone-mediated control of lateral root development.