Snakin-2, an Antimicrobial Peptide from Potato Whose Gene Is Locally Induced by Wounding and Responds to Pathogen Infection

Abstract

The peptide snakin-2 (StSN2) has been isolated from potato (Solanum tuberosum cv Jaerla) tubers and found to be active (EC 50 ϭ 1-20 m) against fungal and bacterial plant pathogens. It causes a rapid aggregation of both Gram-positive and Gram-negative bacteria. The corresponding StSN2 cDNA encodes a signal sequence followed by a 15-residue acidic sequence that precedes the mature StSN2 peptide, which is basic (isoelectric point ϭ 9.16) and 66 amino acid residues long (molecular weight of 7,025). The StSN2 gene is developmentally expressed in tubers, stems, flowers, shoot apex, and leaves, but not in roots, or stolons, and is locally up-regulated by wounding and by abscisic acid treatment. Expression of this gene is also up-regulated after infection of potato tubers with the compatible fungus Botritys cinerea and down-regulated by the virulent bacteria Ralstonia solanacearum and Erwinia chrysanthemi. These observations are congruent with the hypothesis that the StSN2 is a component of both constitutive and inducible defense barriers.An important component of plant defense is a diverse set of constitutive and pathogen-inducible antimicrobial compounds that includes the so-called pathogenesis-related proteins, several families of antimicrobial peptides, a variety of chemically diverse organic compounds classified as phytoalexins and phytoanticipins, and certain active oxygen and nitrogen species (Osbourn, 1996(Osbourn, , 1999 Broekaert et al., 1997;Kombrink and Somssich, 1997; García-Olmedo et al., 1998). Accumulation of these compounds and the ability of a given pathogen to deal with them may be decisive for the outcome of the interaction (Titarenko et al., 1997a;Ló pez-Solanilla et al., 1998Miguel et al., 2000; Alamillo and García-Olmedo, 2001;García-Olmedo et al., 2001). Thus, it has been shown that increased levels of certain antimicrobial peptides, either through overexpression of the corresponding genes or by appropriate exogenous treatments, result in enhanced tolerance to particular pathogens (Carmona et al., 1993; Terras et al., 1995; Epple et al., 1997;Molina and García-Olmedo, 1997; Holtorf et al., 1998; Thomma et al., 1998 Thomma et al., , 1999.Furthermore, pathogen mutants that are sensitive to antimicrobial peptides show decreased virulence when inoculated in the plant (Titarenko et al., 1997a; Ló pez-Solanilla et al., 1998).Several families of antimicrobial peptides have been characterized in plants ( García-Olmedo et al., 1992, 1995 Broekaert et al., 1997). The majority of them are Cys-rich and their globular structure is stabilized by disulphide bridges, although linear Gly-/His-rich and macrocyclic Cysknot peptides have also been recently identified (Tam et al., 1999;Park et al., 2000). The peptides are generally encoded by multigenic families in which some genes are developmentally regulated in certain tissues, whereas others are pathogen inducible, and a number of them show both constitutive and pathogen-inducible expression (García-Olmedo et al., 1995 Broekaert et al., 1997).In a previous...

Expression, purification and characterization of the recombinant cysteine-rich antimicrobial peptide snakin-1 in Pichia pastoris

“…These peptides exhibit antimicrobial actions on target cells in various ways, such as by perturbation of the microbial cell membrane, or by inhibition of the synthesis of nucleic acids, proteins, enzymes, and cell-wall components that are essential for the survival of microorganisms [10]. Whether expressed constitutively in certain tissues or induced in response to pathogens [11,12], most AMPs share several common characteristics: they are small peptides (12-100 amino acids), have a net positive charge (+2 to +9), and are amphipathic and cysteine-rich with a disulfide bond-stabilized structure [5,13].…”

“…Many AMPs are cysteine-stabilized and these have been classified into several families [14], including cyclotides [15], defensins [16], hevein-like peptides [17], lipid transfer proteins [18], and snakins [11,19]. The snakin family is a novel plant antimicrobial peptide family which shows good similarity with the members of the gibberellic acid stimulated transcript (GAST) and gibberellic acid stimulated in Arabidopsis (GASA) protein families in Arabidopsis [20].…”

“…These disulfide bonds are thought to be important for maintaining their tertiary structure and also responsible for their biological activity [13,24,25]. In previous studies, snakin peptides from potato (Solanum tuberosum) were found to exert strong antimicrobial activity against phytopathogens [11,19,24,26] and animal pathogens [27]. However, little is known about their mechanism of action against target organisms.…”

“…Until now, however, neither experimental information related to the 3-D structure nor the complete disulfide bridge pattern of the snakin family has been published. The second snakin peptide, snakin-2 (SN-2), was also isolated from potato tubers [11]. Although the amino acid sequence of SN-2 is only 38% identical to that of SN-1, both snakin peptides exhibit a similar spectrum of activity against microorganisms [11].…”

“…The second snakin peptide, snakin-2 (SN-2), was also isolated from potato tubers [11]. Although the amino acid sequence of SN-2 is only 38% identical to that of SN-1, both snakin peptides exhibit a similar spectrum of activity against microorganisms [11]. Both cause rapid aggregation of pathogens, although this response is not directly related with their antimicrobial activity [11,26].…”