A Critical Role of Sodium Flux via the Plasma Membrane Na⁺/H⁺ Exchanger SOS1 in the Salt Tolerance of Rice

Abstract

Rice (Oryza sativa) stands among the world's most important crop species. Rice is salt sensitive, and the undue accumulation of sodium ions (Na +) in shoots has the strongest negative correlation with rice productivity under long-term salinity. The plasma membrane Na + /H + exchanger protein Salt Overly Sensitive 1 (SOS1) is the sole Na + efflux transporter that has been genetically characterized to date. Here, the importance of SOS1-facilitated Na + flux in the salt tolerance of rice was analyzed in a reversegenetics approach. A sos1 loss-of-function mutant displayed exceptional salt sensitivity that was correlated with excessive Na + intake and impaired Na + loading into the xylem, thus indicating that SOS1 controls net root Na + uptake and long-distance Na + transport to shoots. The acute Na + sensitivity of sos1 plants at low NaCl concentrations allowed analysis of the transcriptional response to sodicity stress without effects of the osmotic stress intrinsic to high-salinity treatments. In contrast with that in the wild type, sos1 mutant roots displayed preferential down-regulation of stress-related genes in response to salt treatment, despite the greater intensity of stress experienced by the mutant. These results suggest there is impaired stress detection or an inability to mount a comprehensive response to salinity in sos1. In summary, the plasma membrane Na + /H + exchanger SOS1 plays a major role in the salt tolerance of rice by controlling Na + homeostasis and possibly contributing to the sensing of sodicity stress.

Coordinated Transport of Nitrate, Potassium, and Sodium

“…On the other hand, a large proportion of Na + ions accumulated in Arabidopsis shoots were loaded into the xylem by transport systems that appeared to couple the movement of Na + to that of nitrate (Alvarez-Aragon and Rodriguez-Navarro, 2017). The nitrate-dependent loading of Na + into the xylem was additive to that of SOS1, a Na/H exchanger mediating Na + efflux at the xylem parenchyma cells (Shi et al, 2002;El Mahi et al, 2019). Nitrate-dependent Na + transport was partially interrupted in the nrt1.1 mutant but not in nrt1.2, implying that unidentified nitrate transporters under the regulation of the NRT1.1 transceptor were involved in this process (Alvarez-Aragon and Rodriguez-Navarro, 2017).…”

Back to the Wild: On a Quest for Donors Toward Salinity Tolerant Rice

“…Overexpression of SOS1 of multiple plant species leads to salt tolerance in plants (Shi et al, 2000;Pardo et al, 2006;Oh et al, 2009;Olías et al, 2009). An OsSOS1 loss of function mutant displayed exceptional salt sensitivity that was correlated with excessive Na + uptake and impaired Na + loading into the xylem (El Mahi et al, 2019). NHXs sequester Na + into vacuoles and are used for osmotic adjustment in salt tolerant plants (Apse et al, 1999;Nieves-Cordones et al, 2016).…”

Salinity Stress-Mediated Suppression of Expression of Salt Overly Sensitive Signaling Pathway Genes Suggests Negative Regulation by AtbZIP62 Transcription Factor in Arabidopsis thaliana

“…The expression level of SOS1 was significantly higher than that of SOS2 and SOS3. A recent study of the plasma membrane Na+/H+ exchanger reported that the rice SOS1 gene plays a pivotal role in the adaptive response to salt tolerance [51]. It is thought that Arabidopsis SOS1 could play a leading role in modulating ion pumping and exchange within the cell during salt stress events.…”