Patellin1 Negatively Modulates Salt Tolerance by Regulating PM Na+/H+ Antiport Activity and Cellular Redox Homeostasis in Arabidopsis.

Soil salinity significantly represses plant development and growth. Mechanisms involved sodium (Na+) extrusion and compartmentation, intracellular membrane trafficking as well as redox homeostasis regulation play important roles in plant salt tolerance. In this study, we report that Patellin1 (PATL1), a membrane trafficking-related protein, modulates salt tolerance in Arabidopsis. The T-DNA insertion mutant of PATL1 (patl1) with an elevated PATL1 transcription level displays a salt-sensitive phenotype. PATL1 partially associates with the plasma membrane (PM) and endosomal system, and might participate in regulating membrane trafficking. Interestingly, PATL1 interacts with SOS1, a PM Na+/H+ antiporter in the Salt-Overly-Sensitive (SOS) pathway, and the PM Na+/H+ antiport activity is lower in patl1 than in Col-0. Furthermore, the reactive oxygen species (ROS) content is higher in patl1 and the redox signaling of antioxidants is partially disrupted in patl1 under salt stress conditions. Artificial elimination of ROS could partially rescue the salt-sensitive phenotype of patl1. Taken together, our results indicate that PATL1 participates in plant salt tolerance by regulating Na+ transport at least in part via SOS1, and by modulating cellular redox homeostasis during salt stress.

UBIQUITIN-SPECIFIC PROTEASES function in plant development and stress responses.

KEY MESSAGE: UBIQUITIN-SPECIFIC PROTEASES play important roles in plant development and stress responses. Protein ubiquitination and deubiquitination are reversible processes, which can modulate the stability, activity as well as subcellular localization of the substrate proteins. UBIQUITIN-SPECIFIC PROTEASE (UBP) protein family participates in protein deubiquitination. Members of UBP family are involved in a variety of physiological processes in plants, as evidenced by their functional characterization in model plant Arabidopsis and other plants. UBPs are conserved in plants and distinct UBPs function in different regulatory processes, although functional redundancies exist between some members. Here we briefly reviewed recent advances in understanding the biological functions of UBP protein family in Arabidopsis, particularly the molecular mechanisms by which UBPs regulate plant development and stress responses. We believe that elucidation of UBPs function and regulation in Arabidopsis will provide new insights about protein deubiquitination and might shed light on the understanding of the mechanistic roles of UBPs in general, which will definitely contribute to crop improvement in agriculture.

Stability and localization of 14-3-3 proteins are involved in salt tolerance in Arabidopsis.

KEY MESSAGE: Salt stress induces the degradation of 14-3-3 proteins, and affects the localization of 14-3-3 λ. Both the modulation of 14-3-3 protein stability and the subcellular localization of these proteins are involved in salt tolerance in plants. Salt tolerance in plants is regulated by multiple signaling pathways, including the salt overly sensitive (SOS) pathway, of which the SOS2 protein is a key component. SOS2 is activated under salt stress to enhance salt tolerance in plants. We previously identified 14-3-3 λ and κ as important regulators of salt tolerance. Both proteins interact with SOS2 to inhibit its kinase activity under normal growth conditions. In response to salt stress, 14-3-3 proteins dissociate from SOS2, releasing its activity and activating the SOS pathway to confer salt tolerance (Zhou et al. Plant Cell 26:1166-1182, 2014). Here we report that salt stress promotes the degradation of 14-3-3 λ and κ, at least in part via the actions of SOS3-like calcium binding protein 8/calcineurin-B-like10, and also decreases the plasma membrane (PM) localization of 14-3-3 λ. Salt stress also partially represses the interaction of SOS2 and 14-3-3 λ at the PM, but activates PM-localized SOS2. Together, these results suggest that, in plants, both the modulation of 14-3-3 stability and the subcellular localization of these proteins in response to salt stress are important for SOS2 activation and salt tolerance. These data provide new insights into the biological roles of 14-3-3 proteins in modulating salt tolerance.