Plant ‘pathogenesis-related’ proteins and their role in defense against pathogens

Abstract

The hypersensitive reaction to a pathogen is one of the most efficient defense mechanisms in nature and leads to the induction of numerous plant genes encoding defense proteins. These proteins include: 1) structural proteins that are incorporated into the extracellular matrix and participate in the confinement of the pathogen; 2) enzymes of secondary metabolism, for instance those of the biosynthesis of plant antibiotics; 3) pathogenesis-related (PR) proteins which represent major quantitative changes in soluble protein during the defense response. The PRs have typical physicochemical properties that enable them to resist to acidic pH and proteolytic cleavage and thus survive in the harsh environments where they occur: vacuolar compartment or cell wall or intercellular spaces. Since the discovery of the first PRs in tobacco many other similar proteins have been isolated from tobacco but also from other plant species, including dicots and monocots, the widest range being characterized from hypersensitively reacting tobacco. Based first on serological properties and later on sequence data, the tobacco PRs have been classified in five major groups. Group PR-1 contains the first discovered PRs of 15-17 kDa molecular mass, whose biological activity is still unknown, but some members have been shown recently to have antifungal activity. Group PR-2 contains three structurally distinct classes of 1,3-beta-glucanases, with acidic and basic counterparts, with dramatically different specific activity towards linear 1,3-beta-glucans and with different substrate specificity. Group PR-3 consists of various chitinases-lysozymes that belong to three distinct classes, are vacuolar or extracellular, and exhibit differential chitinase and lysozyme activities. Some of them, either alone or in combination with 1,3-beta-glucanases, have been shown to be antifungal in vitro and in vivo (transgenic plants), probably by hydrolysing their substrates as structural components in the fungal cell wall. Group PR-4 is the less studied, and in tobacco contains four members of 13-14.5 kDa of unknown activity and function. Group PR-5 contains acidic-neutral and very basic members with extracellular and vacuolar localization, respectively, and all members show sequence similarity to the sweet-tasting protein thaumatin. Several members of the PR-5 group from tobacco and other plant species were shown to display significant in vitro activity of inhibiting hyphal growth or spore germination of various fungi probably by a membrane permeabilizing mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

An insight into the sialotranscriptome of the non-blood feeding Toxorhynchites amboinensis mosquito

“…The CAP family is related to venom allergens in social wasps and ants (Hoffman, 1993;King and Spangfort, 2000) and to antifungal proteins in plants (Stintzi et al, 1993;Szyperski et al, 1998). Members of this protein family are found in the SG of many bloodsucking insects and ticks (Francischetti et al, 2002;Li et al, 2001;Valenzuela et al, 2002b).…”

Prediction of Glycosylphosphatidylinositol-Anchored Proteins in Arabidopsis. A Genomic Analysis

“…All 16 predicted GPI-anchored glucanases have an acidic pI, consistent with an extracellular localization. The ␤-1,3-glucanases are "pathogenesis-related" proteins that are induced in response to pathogen attack (Vogeli-Lange et al, 1988;Stintzi et al, 1993;Beffa and Meins, 1996). They may break down ␤-1,3-glucan of fungal cell walls, which in turn can produce elicitors to trigger a complex defense response and increase resistance to infection (Klarzynski et al, 2000).…”

A Review: Biological and Technological Functions of Barley Seed Pathogenesis-Related Proteins (PRs)

“…PRs have evolved to survive in the hostile conditions of vacuolar compartments or extracellular spaces, where they are often localized 321 . They are usually small proteins, up to 50 kDa, with a compact structure stabilized by several disulphide bonds, either acidic or basic, often with extreme pIs.…”

“…Due to a common compact structure, usually stabilized by disulphide bridges, PRs are resistant towards proteolysis and elevated temperatures, and remain soluble at low pH, where most of the other plant proteins are denatured. Evolved to be inherently stable in extreme conditions of vacuolar, apoplastic or intercellular spaces where they are usually localized 321 , PRs are able to survive harsh conditions of different technological processes. Certain barley seed PRs endure malting, mashing and wort boiling.…”