Distinct Roles of N-Terminal Fatty Acid Acylation of the Salinity-Sensor Protein SOS3
Irène Villalta, Elena Gómez García, Dámaso Hornero‐Méndez, Raúl Carranco, Carlos Tello, Imelda Mendoza, Anna De Luca, Zaida Andrés, Karin Schumacher, José M. Pardo, Francisco J. Quintero
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.