The plasma membrane Na ⁺ /H ⁺ antiporter SOS1 interacts with RCD1 and functions in oxidative stress tolerance in Arabidopsis

Abstract

The adverse effects of high salt on plants include Na ؉ toxicity and hyperosmotic and oxidative stresses. The plasma membrane-localized Na ؉ ͞H ؉ antiporter SOS1 functions in the extrusion of toxic Na ؉ from cells and is essential for plant salt tolerance. We report here that, under salt or oxidative stress, SOS1 interacts through its predicted cytoplasmic tail with RCD1, a regulator of oxidativestress responses. Without stress treatment, RCD1 is localized in the nucleus. Under high salt or oxidative stress, RCD1 is found not only in the nucleus but also in the cytoplasm. Like rcd1 mutants, sos1 mutant plants show an altered sensitivity to oxidative stresses. The rcd1mutation causes a decrease in salt tolerance and enhances the salt-stress sensitivity of sos1 mutant plants. Several genes related to oxidative-stress tolerance were found to be regulated by both RCD1 and SOS1. These results reveal a previously uncharacterized function of a plasma membrane Na ؉ ͞H ؉ antiporter in oxidativestress tolerance and shed light on the cross-talk between the ion-homeostasis and oxidative-stress detoxification pathways involved in plant salt tolerance.salt stress ͉ reactive oxygen species ͉ hydrogen peroxide stress

The Paralogous GenesRADICAL-INDUCED CELL DEATH1andSIMILAR TO RCD ONE1Have Partially Redundant Functions during Arabidopsis Development

“…It has previously been reported that rcd1 is involved in response to a number of abiotic stresses (Overmyer et al, 2000(Overmyer et al, , 2005Ahlfors et al, 2004;Fujibe et al, 2004Fujibe et al, , 2006Katiyar-Agarwal et al, 2006). The rcd1-3 allele behaves similarly to the previously described alleles by displaying increased resistance to chloroplastic reactive oxygen species (ROS) induced by paraquat (Table I).…”

“…We independently isolated a T-DNA insertion allele of RCD1, rcd1-3, which has previously been described (Katiyar-Agarwal et al, 2006). This allele can be complemented by a 35S::RCD1 transgene (see Fig.…”

“…Intriguingly, the 35S::RCD1 transgene was able to complement all tested rcd1-2 phenotypes (Fujibe et al, 2006). A third RCD1 allele, rcd1-3, has been identified (Katiyar-Agarwal et al, 2006) and displays similar phenotypes to rcd1-1 and rcd1-2, although it has not been fully characterized. Taken together, the available data suggest that there is an optimal level of RCD1 activity/level for normal development and stress response.…”

Structural Insights on the Plant Salt-Overly-Sensitive 1 (SOS1) Na+/H+ Antiporter

“…5 Both EM reconstruction of SOS1 show that the cytosolic moiety forms an elongated structure that extends about 50 Å away from the TM domain. In this sense, the overall shape and size of the cytosolic moiety is extended enough to serve as a docking site for the regulatory SOS2 5 and MPK6 9 kinases and also to other proteins such as RCD1 10 thus, merging different stress signals. However, the volume of this region in the class 1 reconstruction is consistent with the size of the SOS1 cytoplasmic domain while the class 2 reconstruction displays smaller size.…”

“…9 In addition, it has been shown that SOS1 interacts with RCD1 and functions in the oxidative stress response. 10 These findings suggest that a variety of protein-protein interactions with the SOS1 cytosolic domain regulate its function. This would imply that SOS1 represents a central hub coordinating different stimuli in response to different stress signals, thus, constituting an important target for biotechnological applications.…”