Distinct Roles of N-Terminal Fatty Acid Acylation of the Salinity-Sensor Protein SOS3

Abstract

The Salt-Overly-Sensitive (SOS) pathway controls the net uptake of sodium by roots and the xylematic transfer to shoots in vascular plants. SOS3/CBL4 is a core component of the SOS pathway that senses calcium signaling of salinity stress to activate and recruit the protein kinase SOS2/CIPK24 to the plasma membrane to trigger sodium efflux by the Na/H exchanger SOS1/NHX7. However, despite the well-established function of SOS3 at the plasma membrane, SOS3 displays a nucleo-cytoplasmic distribution whose physiological meaning is not understood. Here, we show that the N-terminal part of SOS3 encodes structural information for dual acylation with myristic and palmitic fatty acids, each of which commands a different location and function of SOS3. N-myristoylation at glycine-2 is essential for plasma membrane association and recruiting SOS2 to activate SOS1, whereas S-acylation at cysteine-3 redirects SOS3 toward the nucleus. Moreover, a poly-lysine track in positions 7–11 that is unique to SOS3 among other Arabidopsis CBLs appears to be essential for the correct positioning of the SOS2-SOS3 complex at the plasma membrane for the activation of SOS1. The nuclear-localized SOS3 protein had limited bearing on the salt tolerance of Arabidopsis. These results are evidence of a novel S-acylation dependent nuclear trafficking mechanism that contrasts with alternative subcellular targeting of other CBLs by S-acylation.

S-acylated and nucleus-localized SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 stabilizes GIGANTEA to regulate Arabidopsis flowering time under salt stress

“…Like GI, SOS3 is a nucleo-cytoplasmic protein ( Batistic et al, 2010 ; Villalta et al, 2021 ). N -myristoylation of SOS3 at Gly-2 is essential for plasma membrane attachment and recruitment of SOS2 for salt tolerance, whereas S -acylation at residue Cys-3 promotes nuclear entry ( Villalta et al, 2021 ).…”

“…Like GI, SOS3 is a nucleo-cytoplasmic protein ( Batistic et al, 2010 ; Villalta et al, 2021 ). N -myristoylation of SOS3 at Gly-2 is essential for plasma membrane attachment and recruitment of SOS2 for salt tolerance, whereas S -acylation at residue Cys-3 promotes nuclear entry ( Villalta et al, 2021 ). Therefore, we determined whether salt stress affected SOS3 S -acylation and tested the influence of N -myristoylation and S -acylation of SOS3 on salt-induced flowering delay.…”

“…Among the 10 CBL proteins of Arabidopsis, dual fatty acid modifications consisting of N -myristoylation and S -acylation contribute to the cellular sorting of CBL1, SOS3/CBL4, CBL5, and CBL9 ( Batistic et al, 2008 ; Batistic et al, 2010 ). N -myristoylation of SOS3 at Gly-2 allows the SOS2-SOS3 complex to associate with the plasma membrane and phosphorylate SOS1 to promote Na + efflux ( Quintero et al, 2002 ; Villalta et al, 2021 ). S -acylation of the cysteine residue adjacent to the myristoylated glycine is thought to enhance the membrane attachment of CBL proteins and to regulate subcellular trafficking from the ER to the plasma membrane ( Batistic et al, 2008 ; Held et al, 2011 ; Saito et al, 2018 ).…”

Exogenous calcium application enhances salt tolerance of sweet sorghum seedlings

“…The first gene to be accidentally discovered during genetic screening of ‘salt overly sensitive’ (SOS) mutants is the Ca 2+ ‐binding protein SOS3 (Liu & Zhu, 1997). SOS3 was identified as the fourth member (designated CBL4) of the Calcineurin B‐like proteins (CBLs), which act as Ca 2+ sensor proteins in many essential plant processes (Kudla et al, 1999; Liu et al, 2020; Manishankar et al, 2018; Villalta et al, 2021). SOS3 binds and activates SOS2 to form a Ca 2+ sensor‐kinase complex that activates Na + /H + antiporter by promoting sodium ion efflux and sodium ion transport over long distances in plants (An et al, 2020; Halfter et al, 2000; Manishankar et al, 2018; Shi et al, 2000).…”

Protein S-acyltransferases and acyl protein thioesterases, regulation executors of protein S-acylation in plants

“…N-myristoylation and S-acylation of calcium signaling participants, CBLs and CPKs, have been well studied. CBL1, 4, 5, and 9, which undergo both N-myristoylation and S-acylation, are localized on the plasma membrane (PM), whereas CBL2, 3, 6, and 10, containing only S-acylation modification at the N-terminal sites, are found on the tonoplast ( Zhou et al, 2013 ; Saito et al, 2018 ; Chai et al, 2020 ; Villalta et al, 2021 ). Mutations at any of these sites significantly diminish the protein localization.…”