Inhibition of the Arabidopsis Salt Overly Sensitive Pathway by 14-3-3 Proteins  

Abstract

The Salt Overly Sensitive (SOS) pathway regulates intracellular sodium ion (Na+) homeostasis and salt tolerance in plants. Until recently, little was known about the mechanisms that inhibit the SOS pathway when plants are grown in the absence of salt stress. In this study, we report that the Arabidopsis thaliana 14-3-3 proteins λ and κ interact with SOS2 and repress its kinase activity. Growth in the presence of salt decreases the interaction between SOS2 and the 14-3-3 proteins, leading to kinase activation in planta. 14-3-3 λ interacts with the SOS2 junction domain, which is important for its kinase activity. A phosphorylation site (Ser-294) is identified within this domain by mass spectrometry. Mutation of Ser-294 to Ala or Asp does not affect SOS2 kinase activity in the absence of the 14-3-3 proteins. However, in the presence of 14-3-3 proteins, the inhibition of SOS2 activity is decreased by the Ser-to-Ala mutation and enhanced by the Ser-to-Asp exchange. These results identify 14-3-3 λ and κ as important regulators of salt tolerance. The inhibition of SOS2 mediated by the binding of 14-3-3 proteins represents a novel mechanism that confers basal repression of the SOS pathway in the absence of salt stress.

14-3-3 λ protein interacts with ADF1 to regulate actin cytoskeleton dynamics in Arabidopsis

“…Under light condition, the hypocotyl length in 14-3-3  was also slightly longer than that of Col-0 ( Figure 1E and F). We previously published that 14-3-3  is a regulator of SOS2 kinase [24]. Consistent with our previous results, the homozygous 14-3-3  mutant contained a T-DNA insertion in the 2nd intron of At5g10450, and a very low amount of transcript was detected by RT-PCR in the mutant plants ( Figure 1G and H).…”

“…In our previous study, the 14-3-3 -GUS expression patterns and the immunoblot assays with 14-3-3  antibodies indicate that 14-3-3  protein ubiquitously expresses in all tissues including hypocotyl [24]. We observed the actin structure of middle hypocotyl cells at the place about 5 mm distance from the root using the plants grown under dark for 5 d (Figure 2A).…”

“…In Arabidopsis, 14-3-3 protein family contains 13 members that interact with various targets involved in regulation of plant growth and development, abiotic and biotic stress responses [23,24]. Previous studies demonstrate that 14-3-3  and  proteins interact with and repress salt overly sensitive 2 (SOS2) activity in the absence of salt stress.…”

“…Previous studies demonstrate that 14-3-3  and  proteins interact with and repress salt overly sensitive 2 (SOS2) activity in the absence of salt stress. The interaction between these 14-3-3 proteins and SOS2 is reduced when plant responds to salt stress in order to activating SOS pathway for salt tolerance [24]. The expression of 14-3-3 psi is specific induced by low temperature [25,26].…”

Structural basis of the regulatory mechanism of the plant CIPK family of protein kinases controlling ion homeostasis and abiotic stress

“…Although the default state of CIPKs is inactive, some degree of autophosphorylation activity has been observed even for dephosphorylated and CBL-unbound CIPKs, which suggests that some CIPKs display basal activity (6). Indeed, it has been shown that the general regulatory factor 14-3-3 proteins (32) interact with CIPK24/SOS2 and repress its basal kinase activity when plants are grown in the absence of salt stress (33).…”