Biochemical characterization of Salt Tolerance-Related Protein (STRP): a new protein involved in cold stress in A. thaliana

Salt tolerance-related protein (STRP) is an A. thaliana uncharacterized protein involved in response to different biotic and abiotic stresses. Identified in a proteomic screen of temperature related protein (Rocco et al., 2013) the information available are really poor. It is involved in response to salt stress and knockout mutant are hypersensitive to this stress (Du et al., 2008). By an anti-STRP polyclonal antibody, obtained on recombinant protein, has been verify that cold stress causes the increase in the protein levels into the cytosol, already after 10 minutes, thanks to the inhibition of proteasome mediated degradation. Subcellular localization of STRP has been determined by the transient expression of protein fused with GFP in A. thaliana protoplasts. STRP in localized into the cytosol, into the nucleus and is also associated to the plasma membrane. Cold stress induces the increase in the protein fraction into the cytosol and nucleus, instead the fraction associated to the membrane decreases. Then both the inhibition of proteasome degradation and the translocation of protein from the membrane contribute to the increase in STRP levels into the cytosol. Into the nucleus the protein is able to bind chromatin and could be also able to interact with chromatin remodelling proteins accordingly with Waidmann et al., 2014. We generated Arabidopsis STRP-overexpressing plants by Agrobacterium-mediated transformation, and we obtained Strp knockout mutants by the Nottingham Arabidopsis Stock Center, to clarify the physiological function of STRP and its role in response to cold stress. Phenotypical analysis of overexpressing plants and strp knockout has been be carried out, and plant responses to cold stress (oxidative damage, membrane lipid modification, production of osmoprotectant solutes, cold-related gene expression) has been evaluated. We also analysed the effects of ABA on knockout plants growth and development and in the stomatal movement, ascertaining the ABA- hyposensitive phenotype of these plants.