| Abstract | Pathogenesis related (PR) proteins, which are induced by various agents ranging from ethylene to pathogens, are structurally diverse and apparently ubiquitous in plants [ 1463856]: they include thaumatin, osmotin, tobacco major and minor PR proteins, alpha-amylase/trypsin inhibitor, and P21 and PWIR2 soybean and wheat leaf proteins. The proteins are involved in systematically acquired resistance and stress response in plants, although their precise role is unknown [1463856]. Thaumatin is an intensely sweet tasting protein (about 100,000 times sweeter than sucrose [7049841]) found in the West African shrub Thaumatococcus daniellii: it is induced by attack by viroids, which are single-stranded unencapsulated RNA molecules that do not code for protein. Like other PR proteins, thaumatin is predicted to have a mainly beta structure, with a high content of beta-turns and little helix [1463856].
Tobacco cells exposed to gradually increased salt concentrations develop a greatly increased tolerance to salt, due to the expression of osmotin, a member of the PR protein family. Wheat plants attacked by barley powdery mildew express a PR protein (PWIR2), which results in resistance against that infection [1650615]. The similarity between this and other PR proteins to the maize alpha-amylase/trypsin inhibitor has suggested that PR proteins may act as some form of inhibitor [1650615]. |
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