natural-products-in-plant-pest-management

Proteinaceous and Polyketide Compounds in Plant Protection 119fungal membranes has been shown for toumatin-like proteins (permatins) ofthe PR-5 class. Overexpression of PR protein genes in plants renders diseaseresistance. For example, the high level expression of PR-1 in transgenictobacco plants promotes control of Perenospora tabacina and Phytophthoranicotiana (Dyakov and Ozeratskovskaya, 2007).Biochemical functions of PR proteins, their role in defence mechanisms,engineering of transgenic plants with enhanced resistance to plant pathogensand characteristics of individual PR proteins have been comprehensivelysurveyed by many researchers (Van Loon, 1985; Loon and Van Strien,1999; Van Punja, 2001; De Lucca et al., 2005; Edreva, 2005; Van Loon et al.,2006; Sels et al., 2008).Proteinic inducers of plant resistance as a promising strategy for greenconsumerizationThe protective effect of some natural compounds against plant diseasesresults from the induction of plant resistance to pathogens rather than frombiocidal activity towards the causative agents. This strategy is worthy of specialconsideration because it avoids a direct effect on a pathogen and involvesa plant-mediated mode of action. This activates the natural defence responsesof plants, minimizing the probability of the targeted pathogens developingresistance.Active defence mechanisms are initiated in plants upon recognition ofstructural and chemical characteristics particular to a pathogen, collectivelyreferred to as pathogen-associated molecular pattern (PAMPs). The PAMPcomponents represented by compounds of different chemical origin werenamed as general elicitors (or general inducers). These elicitors initiate a conservedset of plant defence responses such as ROS production, deposition ofcallose, protein phosphorylation, and transcriptional activation of earlyresponse genes, resulting in PAMP-triggered immunity or induced resistance.Natural compounds conferring disease resistance on plants in themanner of general elicitors is of interest because of the non-specific characterof the induced resistance – lots of pathogens can be controlled with one activecompound. The success of applying elicitor compounds is directly dependenton understanding their properties and mechanisms of action. As well asall other biogenic or abiogenic, general or specific inducers, proteinaceouselicitors produced by plant pathogens (e.g. glicoproteins, flagellins, elongationfactor Tu, elicitins and transglutaminases from Phytophthora spp., proteinsand peptides from Cladosporium flavum, monolicollin, cold shockproteins, harpins etc.) are the subject of genetic and biochemical research ofsignalling pathways and molecular mechanisms underlying plant resistanceto diseases. Non-protein small compounds (plant signalling molecules andhormones) participating in signalling as well as chemical compounds thathave been found to mimic elicitors are also being studied in this way. Transgenicplants with genes encoding microbial elicitors (e.g. elicitins) are createdfor research purposes using biotechnological methods.