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.
Highlights
IntroductionPlants are constantly challenged by abiotic and biotic stress factors. Salinization is an increasingly common abiotic stress, leading to reduced growth, impaired development, and significantly reduced crop yields [1]
In nature, plants are constantly challenged by abiotic and biotic stress factors
The coupled protein was incubated with a soluble protein extract prepared from Arabidopsis leaves to interact with putative binding partners
Summary
Plants are constantly challenged by abiotic and biotic stress factors. Salinization is an increasingly common abiotic stress, leading to reduced growth, impaired development, and significantly reduced crop yields [1]. Since sodium chloride (NaCl) is present in most types of soil, flowering plants have developed a sophisticated multifactorial strategy to withstand situations in which salt is present in excess. This strategy can be sub-categorized into at least three modes, namely (i) the avoidance of salt uptake, (ii) Na+ export from the cell across the plasma membrane, and (iii) internal cellular compartmentalization into the central vacuole [2,3,4]. Plants have various morphological and structural features that limit Na+ uptake into the plant body, and the intracellular sequestration of salt is catalyzed by electroneutral Na+/H+ antiporters of the NHX (Na+/H+ Exchanger) protein family. Subsequent studies revealed that the SOS system of flowering plants consists of three components: the Na+/H+ exchanger SOS1; the protein kinase SOS2, which activates SOS1; and SOS3, a plasma membrane-located calcium sensor that induces SOS2 activity upon the onset of salt stress [7]
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