Characterization of Osmotin

Abstract

ABSTRACEOsmotin is a cationic protein with a pl2 value >8.2 and accounts for 10 to 12% of total cellular protein (as determined by spectrophotometric measurement of Coomassie stained gels) in NaCl and polyethylene glycol adapted tobacco cells (23). In unstressed unadapted cells, an immunologically related 26 kD protein with a lower pl is also synthesized but is not accumulated under normal growth conditions (23). Osmotin synthesis is regulated by abscisic acid, but its accumulation depends on adjustment of the cells to NaCl or to water stress (24). Others using cells obtained from our laboratory, have confirmed our observation of the accumulation of this protein in salt adapted cells (10, 16). We have isolated osmotin from NaCl adapted tobacco cells in sufficient quantities for further characterization. In this report we describe a simple and rapid procedure for purification oftwo forms ofosmotin, some oftheir properties and localization within the cell, and the occurrence of significant amino acid sequence homology between osmotin, the sweet protein, thaumatin, and two other stress-related proteins.MATERIALS AND METHODS Cell Culture. Cell suspension cultures of tobacco (Nicotiana tabacum L. var Wisconsin-38) adapted to 25 g/L NaCl (S-25 cells) were maintained in our laboratory as described (12). These cells were harvested and stored as dry powders after washing in cold acetone (23

Colonization of the Arabidopsis rhizosphere by fluorescent Pseudomonas spp. activates a root-specific, ethylene-responsive PR-5 gene in the vascular bundle

“…A large number of PR-5 proteins from different plant species has been isolated and characterized (Anzˇlovar and Dermastia, 2003), all of which show similarity to the sweet-tasting protein thaumatin present in the fruits of the tropical shrub Thaumatococcus danielii (Van der Wel and Loeve, 1972). Several PR-5 proteins have been shown to possess antimicrobial activity in vitro (Woloshuk et al, 1991;Anzˇlovar and Dermastia, 2003), or in vivo (Liu et al, 1994), or appear to be involved in osmotic adaptation (Singh et al, 1987;Anzˇlovar and Dermastia, 2003). Besides constitutive and tissue-specific PR-5 genes, many PR-5 genes are induced upon biotic or abiotic stresses (Van Loon and Van Strien, 1999).…”

Stress proteins on the yeast cell surface determine resistance to osmotin, a plant antifungal protein

“…Osmotin was purified from salt-adapted tobacco cell suspension cultures (Nicotiana tabacum L. var. Wisconsin 38) to apparent homogeneity as described (2). PR-5 proteins A8 and A9 were purified similarly from cell suspension cultures of the plant Atriplex nummularia.…”

“…For example, the bases for activity against fungi of thionins, defensins, PR-1, PR-4, and PR-5 proteins are not known (1). Osmotin is a member of the PR-5 family that was originally identified as the predominant protein that accumulated in tobacco cells as a function of osmotic adaptation (2). Subsequently, osmotin and other osmotin-like proteins were shown to have antifungal activity in vitro against a broad range of fungi, including several plant pathogens (1).…”

Two antifungal thaumatin‐like proteins from barley grain

“…One family of PR-proteins (often called PR5 or osmotins) contains proteins of M, -22 kDa, which are homologous with the intensely sweet protein thaumatin from fruits of Thntrmatococcw daniellii Benth and they are therefore called thaumatin-like or TL-proteins [l]. These proteins and their expression have been studied in some detail in tobacco [2][3][4] and potato [S] but their biological function is unknown. Recently a TLPR-protein was identified in barley leaves challenged with an incompatible race of mildew [6].…”