Regulation of durum wheat Na+/H+ exchanger TdSOS1 by phosphorylation

Abstract

We have identified a plasma membrane Na(+)/H(+) exchanger from durum wheat, designated TdSOS1. Heterologous expression of TdSOS1 in a yeast strain lacking endogenous Na(+) efflux proteins showed complementation of the Na(+)- and Li(+)-sensitive phenotype by a mechanism involving cation efflux. Salt tolerance conferred by TdSOS1 was maximal when co-expressed with the Arabidopsis protein kinase complex SOS2/SOS3. In vitro phosphorylation of TdSOS1 with a hyperactive form of the Arabidopsis SOS2 kinase (T/DSOS2∆308) showed the importance of two essential serine residues at the C-terminal hydrophilic tail (S1126, S1128). Mutation of these two serine residues to alanine decreased the phosphorylation of TdSOS1 by T/DSOS2∆308 and prevented the activation of TdSOS1. In addition, deletion of the C-terminal domain of TdSOS1 encompassing serine residues at position 1126 and 1128 generated a hyperactive form that had maximal sodium exclusion activity independent from the regulatory SOS2/SOS3 complex. These results are consistent with the presence of an auto-inhibitory domain at the C-terminus of TdSOS1 that mediates the activation of TdSOS1 by the protein kinase SOS2. Expression of TdSOS1 mRNA in young seedlings of the durum wheat variety Om Rabia3, using different abiotic stresses (ionic and oxidative stress) at different times of exposure, was monitored by RT-PCR.

The Role of Na+ and K+ Transporters in Salt Stress Adaptation in Glycophytes

“…Overexpression of the truncated TdSOS1 protein in Arabidopsis showed superior tolerance to Na + and Li + stress compared with WT TdSOS1 and AtSOS1 (Feki et al, 2014). These studies on TdSOS1 show that contrary to initial reports of the function of SOS1 as a Na + /H + antiporter (Feki et al, 2011, 2014), it is now clear that at least in TdSOS1, the function also includes Li + efflux. Furthermore, Garciadeblás et al (2007) showed that SOS1 mediated low-affinity K + transport in Escherichia coli , but it failed to complement K + uptake deficiency in yeast, which leads to the question: is SOS1 involved in K + nutrition?…”

“…Although in the SOS pathway SOS1 is effectively involved in Na + transport, the SOS3/SOS2 or SCaBP/SOS2 complex is a determinant of its antiporter activity, implying that functional studies on SOS1 activity would require the other two components (Quintero et al, 2002) (Figure 2). However, it is now possible to circumvent this requirement, as it has been shown that deleting the C-terminal domain (auto-inhibitory and SOS2 phosphorylation site) of the Triticum durum TdSOS1 renders the protein more hyperactive than the native protein and functions in a way that is independent of SOS3/SOS2 phosphorylation (Feki et al, 2011, 2014). Overexpression of the truncated TdSOS1 protein in Arabidopsis showed superior tolerance to Na + and Li + stress compared with WT TdSOS1 and AtSOS1 (Feki et al, 2014).…”

Root vacuolar Na+ sequestration but not exclusion from uptake correlates with barley salt tolerance

“…Also, Thellungiella, a halophyte relative to Arabidopsis, showed higher SOS1 at both transcriptional and protein levels (Vera-Estrella et al, 2005;Kant et al, 2006;Oh et al, 2009;Taji et al, 2010). However, Feki et al (2011) showed that overexpressing TdSOS1 in Arabidopsis did not result in any significant enhancement of the salt stress tolerance in transgenic plants as compared with the performance of lines transformed with empty vectors. Is this because the wrong cell type was targeted?…”

“…However, Feki et al . () showed that overexpressing TdSOS1 in Arabidopsis did not result in any significant enhancement of the salt stress tolerance in transgenic plants as compared with the performance of lines transformed with empty vectors. Is this because the wrong cell type was targeted?…”

Physiological and molecular mechanisms mediating xylem Na+ loading in barley in the context of salinity stress tolerance

“…Also essential for plants is a delivery of sufficient amounts of K + to the shoot, to maintain normal cell metabolism in photosynthetically active mesophyll cells. With the application of molecular biology techniques, several candidate genes of ion transporters relevant to xylem ion loading such as Na + /H + antiporter (SOS1; Shi et al, ; Shi et al, ; Feki et al, ; Feki et al, ), high‐affinity Na + /K + ‐permeable transporter (HKT; reviewed by Horie et al, ), chloride cation co‐transporter (CCC; Colmenero‐Flores et al, ) and Shaker‐like outward channel (SKOR; Gaymard et al, ) were identified and characterized. All these transporters were found to potentially mediate xylem K + and Na + loading.…”