The unconventional P-loop NTPase OsYchF1 and its regulator OsGAP1 play opposite roles in salinity stress tolerance

Abstract

YchF proteins are a group of mysterious but ubiquitous unconventional G-proteins found in all kingdoms of life except Archaea. Their functions have been documented in microorganisms, protozoa and human, but those of plant YchF homologues are largely unknown. Our group has previously shown that OsYchF1 and its interacting protein, OsGAP1, play opposite roles in plant defense responses. OsGAP1 was found to stimulate the GTPase/ATPase activities of OsYchF1 and regulate its subcellular localization. In this report, we demonstrate that both OsYchF1 and OsGAP1 are localized mainly in the cytosol under NaCl treatment. The ectopic expression of OsYchF1 in transgenic Arabidopsisthaliana leads to reduced tolerance towards salinity stress, while the ectopic expression of OsGAP1 has the opposite effect. Similar results were also obtained with the Arabidopsis homologues, AtYchF1 and AtGAP1, by using AtGAP1 overexpressors and underexpressors, as well as an AtYchF1-knockdown mutant. OsYchF1 and OsGAP1 also exhibit highly significant effects on salinity-induced oxidative stress tolerance. The expression of OsYchF1 suppresses the anti-oxidation enzymatic activities and increases lipid peroxidation in transgenic Arabidopsis, and leads to the accumulation of reactive oxygen species (ROS) in tobacco BY-2 cells, while the ectopic expression of OsGAP1 has the opposite effects in these two model systems. Using the transgenic Arabidopsis and transgenic BY-2 cell systems, we showed that OsYchF1 plays a negative role in salinity stress response, probably via suppression of the anti-oxidation enzymatic activities, resulting in lipid peroxidation and accumulation of ROS. Its interaction partner OsGAP1 plays an opposite role. We also demonstrated the homologue of OsYchF1 and OsGAP1 in Arabidopsis thaliana (AtYchF1 and AtGAP1, respectively) may play similar roles as their rice counterparts. Therefore, our works have added new dimensions to the functional roles of plant YchF proteins and their regulators. © 2013 John Wiley & Sons Ltd.