14-3-3 Proteins and Other Candidates form Protein-Protein Interactions with the Cytosolic C-terminal End of SOS1 Affecting Its Transport Activity

Abstract

The plasma membrane transporter SOS1 (SALT-OVERLY SENSITIVE1) is vital for plant survival under salt stress. SOS1 activity is tightly regulated, but little is known about the underlying mechanism. SOS1 contains a cytosolic, autoinhibitory C-terminal tail (abbreviated as SOS1 C-term), which is targeted by the protein kinase SOS2 to trigger its transport activity. Here, to identify additional binding proteins that regulate SOS1 activity, we synthesized the SOS1 C-term domain and used it as bait to probe Arabidopsis thaliana cell extracts. Several 14-3-3 proteins, which function in plant salt tolerance, specifically bound to and interacted with the SOS1 C-term. Compared to wild-type plants, when exposed to salt stress, Arabidopsis plants overexpressing SOS1 C-term showed improved salt tolerance, significantly reduced Na+ accumulation in leaves, reduced induction of the salt-responsive gene WRKY25, decreased soluble sugar, starch, and proline levels, less impaired inflorescence formation and increased biomass. It appears that overexpressing SOS1 C-term leads to the sequestration of inhibitory 14-3-3 proteins, allowing SOS1 to be more readily activated and leading to increased salt tolerance. We propose that the SOS1 C-term binds to previously unknown proteins such as 14-3-3 isoforms, thereby regulating salt tolerance. This finding uncovers another regulatory layer of the plant salt tolerance program.

Cold-Triggered Induction of ROS- and Raffinose Metabolism in Freezing-Sensitive Taproot Tissue of Sugar Beet

“…Ions and amino acids were measured according to Duscha et al (2020). Anions and cations were also measured in a 761 Compact IC system (Metrohm and Herisau, Switzerland).…”

Ion Homeostasis and Metabolome Analysis of Arabidopsis 14-3-3 Quadruple Mutants to Salt Stress

“…Na + and K + homeostasis in Arabidopsis under salt stress has also been found to be improved by the coordinated expression of AtHKT1;1 and AtSOS1 (Wang et al, 2014b ). Furthermore, 14-3-3 acts as an upstream regulator of the SOS pathway via not only interacting with and inhibiting SOS2 activity, but also reducing SOS1 transporter activity (Duscha et al, 2020 ). It has also been reported that members of the non-epsilon group, 14-3-3 KAPPA and LAMBDA, interact with and repress the activity of SOS2 in the absence of salt (Zhou et al, 2014 ; Yang et al, 2019 ).…”

“…These findings suggest that 14-3-3 and SOS3 proteins coordinately activate/inactivate the downstream protein kinases SOS2 and PKS5 to regulate cellular Na + homeostasis. Furthermore, the overexpression of the plasma membrane transporter SOS1 C-term leads to the sequestration of inhibitory 14-3-3 proteins, which makes SOS1 more activated and thereby improving salt tolerance in Arabidopsis (Duscha et al, 2020 ). Arabidopsis has a single gene that encodes the HKT1 protein, which is expressed in root stellar cells and controls the root:shoot allocation of Na + by means of Na + retrieval from the xylem (Xue et al, 2011 ).…”

Halotropism: Phytohormonal Aspects and Potential Applications

“…The unknown sodium-specific sensor responsible for halotropic response is expected to sense the intracellular Na + concentration, because the sos1 mutant, which contains higher intracellular Na + (Shi et al, 2002) showed an enhanced halotropic response (Galvan-Ampudia et al, 2013). New findings suggest that 14-3-3 proteins and other candidates could affect the transport activity of SOS1 forming protein-protein interactions with its cytosolic C-terminal end, enhancing our knowledge of this protein involved in salt avoidance mechanisms of roots (Duscha et al, 2020). Comparing the transcript levels of SOS1 in Eutrema (Thellungiella) species, the halophyte relatives of Arabidopsis revealed that the basal and salt stressed induced expression of SOS1 was higher compared to the glycophytes (Oh et al, 2009), suggesting that different magnitude of Na + sensing and regulation of halotropic events in halophytes.…”