PR Proteins: Key Genes for Engineering Disease Resistance in Plants

PR proteins are the proteins that are structurally diverse but are induced by the invading phytopathogens (bacteria, fungi, viruses, nematodes, etc.), and they have been classified into 17 major families (PR1, PR2, PR3–PR17). Functionally they have been classified into thaumatin/osmotin-like proteins, chitinases, glucanases, defensins, thionins, oxalate oxidase, oxalate oxidase-like proteins/germin-like proteins and lipid transfer proteins and so forth. It has been found that besides providing resistance against invading plant pathogens, they also provide tolerance against various abiotic stresses. Recently, the transgenic overexpression of the PR proteins in crop plants has been found useful in enhancing resistance against plant pathogens. Moreover, many regulatory components of PR proteins have also been reported. Although some PR proteins reduce mycotoxin levels in foodstuffs and act as food preservatives, still PR overexpressing transgenics also have some human health related concerns. Some PR proteins are reported to be allergens/potential allergens to humans. Therefore, the careful evaluation of PR overexpressing transgenic in terms of their toxicity or allergenicity may be evaluated before commercialising them as future genetically modified crops.