natural-products-in-plant-pest-management

118 L.A. ShcherbakovaAt least 14 genes encoding different protease inhibitors alone or incombination with other heterologous genes have been reported to be transferredinto cultured plants, which showed increased resistance predominantlyto insects (Valuyeva and Mosolov, 2004). Plant protease inhibitorshave also been used to engineer resistance against viruses in transgenicplants. For example, expression of the gene encoding the cysteine proteinaseinhibitor from rice, oryzacystatin, by transgenic tobacco was found to conferresistance against tobacco etch virus and potato Y virus, replication of whichdepends on cysteine proteinase activity (Valuyeva and Mosolov, 2004; Habiband Khalid, 2007).In the green consumerization context, it is important that some of theavailable proteinase inhibitors are inactive for non-pathogenic microorganismsand do not inhibit activity of proteinases of animal origin. Thus, chestnutcystatin, which strongly inhibits the protease activity and the growth ofpathogenic B. cinerea, Colletotrichum graminicola, and Stagonospora nodorum,has no effect on the protease activity and the growth of the saprophyte Trichodermaviride (Pernas et al., 1999), and a proteinase inhibitor extracted frombean seeds specifically suppresses serine proteinase of pathogenic C. lindemuthianumbut does not influence animal trypsin and chymotrypsin activity(Valuyeva and Mosolov, 2004). Non-specific antipathogenic activity of proteaseinhibitors suggests that transgenic crops producing inhibitors of insecticidalor nematicidal proteinases may be incorporated into integratedsystems of plant protection against pests and pathogens. A further advantageof this approach is the possibility that inhibitory activity against proteinasescould be combined with the insecticidal activity of lectins, resulting in asynergistic antipathogenic effect.PR proteinsPlants have numerous defence mechanisms that are activated in response topathogen attacks, abiotic stresses and chemicals that mimic pathogenchallenge. Production of proteins related to pathogenesis (PR proteins) is onesuch inducible mechanism (Van Loon et al., 1994; Van Loon et al., 2006). Theseproteins are not detectable at all or are present only at basal concentrationsin healthy plant tissues. Since the term PR proteins based on the abovecharacteristics was often used for all constitutive plant proteins for whichcontent or increasing activity was induced by microorganisms, the new term‘inducible defence-related proteins’ was recently introduced (Van Loon et al.,2006).PR proteins consist of a large variety of families with members that differin occurrence, expression and biological activities; they are divided into 17classes (Sels et al., 2008). A range of the above-mentioned plant proteins andpeptides such as chitinases, β-1,3-glucanases, peroxidase, defensins and proteinaseinhibitors are PR proteins and vice versa; some typical PR proteinsare antimicrobial and inhibit pathogen growth in vitro. For instance, tobaccoPR-1a is antifungal, and tomato proteins of the PR-1 family inhibit zoosporegermination and reduce pathogenicity of P. infestans. The ability to disrupt