SOS3 Function in Plant Salt Tolerance Requires N-Myristoylation and Calcium Binding

Abstract

The salt tolerance gene SOS3 (for salt overly sensitive3) of Arabidopsis is predicted to encode a calcium binding protein with an N-myristoylation signature sequence. Here, we examine the myristoylation and calcium binding properties of SOS3 and their functional significance in plant tolerance to salt. Treatment of young Arabidopsis seedlings with the myristoylation inhibitor 2-hydroxymyristic acid caused the swelling of root tips, mimicking the phenotype of the salt-hypersensitive mutant sos3-1 . In vitro translation assays with reticulocyte showed that the SOS3 protein was myristoylated. Targeted mutagenesis of the N-terminal glycine-2 to alanine prevented the myristoylation of SOS3. The functional significance of SOS3 myristoylation was examined by expressing the wild-type myristoylated SOS3 and the mutated nonmyristoylated SOS3 in the sos3-1 mutant. Expression of the myristoylated but not the nonmyristoylated SOS3 complemented the salt-hypersensitive phenotype of sos3-1 plants. No significant difference in membrane association was observed between the myristoylated and nonmyristoylated SOS3. Gel mobility shift and 45 Ca 2 ϩ overlay assays demonstrated that SOS3 is a unique calcium binding protein and that the sos3-1 mutation substantially reduced the capacity of SOS3 to bind calcium. The resulting mutant SOS3 protein was not able to interact with the SOS2 protein kinase and was less capable of activating it. Together, these results strongly suggest that both N-myristoylation and calcium binding are required for SOS3 function in plant salt tolerance.

Salt-induced subcellular kinase relocation and seedling susceptibility caused by overexpression of Medicago SIMKK in Arabidopsis

“…Supporting evidence that the process of activated MAPK relocation to membrane targets may be related to plant adaptation strategies to salt stress comes from studies of the salt overly sensitive (SOS) pathway. Within this pathway, a complex of SOS2, a Ser/Thr protein kinase (Liu et al , 2000), with SOS3, a myristoylated calcium-binding protein (Ishitani et al , 2000), phosphorylates and activates the transport activity of SOS1, a plasma membrane Na + /H + antiporter (Shi et al , 2000; Qiu et al , 2002). MPK6 phosphorylates and activates SOS1, whilst the MAPK module encompassing MPK6 is located at the plasma membrane (Yu et al , 2010; Kim et al , 2012).…”

Calcineurin B-like Protein CBL10 Directly Interacts with TOC34 (Translocon of the Outer Membrane of the Chloroplasts) and Decreases Its GTPase Activity in Arabidopsis

“…It is obvious that the interaction alone is not enough to modulate the TOC34 enzyme activity. This type of Ca 2+ dependency was also observed in other CBL members: CBL2 and CBL4 interacted with CIPK14 and CIPK24, respectively, regardless of Ca 2+ , and yet Ca 2+ binding was essential for the CBL members to activate their target kinases (Halfter et al, 2000; Ishitani et al, 2000; Akaboshi et al, 2008). Crystal structure analyses of CBL4 and CIPK24 provided a useful insight into the molecular mechanism underlying CBL4-mediated activation of CIPK24 (Sánchez-Barrena et al, 2005, 2007).…”

Development and Genetic Characterization of A Novel Herbicide (Imazethapyr) Tolerant Mutant in Rice (Oryza sativa L.)

“…One kilogram seeds of a drought tolerant upland rice variety, Nagina 22 (N22) was treated with 0.8% EMS to raise M 1 (Mohapatra et al 2014). N22 was chosen for mutagenesis for two reasons: 1. it is an upland variety sensitive to Imazethapyr spray; 2.…”