natural-products-in-plant-pest-management

266 S. HettiarachiRecombinant gene technology in natural productsRecombinant gene technology is perhaps the most wonderful tool a biotechnologistever had. Conventional breeding of plants and animals canbring the genes of two different but closely related individuals togetherthrough the fusion of two gametes in sexual reproduction. The nuclearDNA of eukaryotic organisms is organized into chromosomes and theincompatibility in chromosome numbers and chromosome morphology isthe main barrier for bringing genes together from different parents to producea hybrid. However, today’s technology is such that the identificationof DNA controlling a particular trait, isolation of that particular DNA, invitro modification of that DNA, inserting the modified DNA into a desiredorganism to express the trait in the new organism, have become possiblein an appropriately equipped laboratory. This is a straightforwardapproach when the final product is a peptide because engineering the basesequence in an open reading frame under proper control units is sufficient.It is a different matter when it comes to more complex molecules, such assecondary metabolites, which are products of a series of biochemical reactionseach mediated by a specific enzyme. The maturation of the moleculemay also involve chemical modifications within the environment of theproducer cell. In order to make breakthroughs in the production of naturalproducts, particularly those that are not peptides, using biotechnology, anunderstanding of the regulation of the secondary metabolite pathwaysinvolved at the levels of products, enzymes and genes, including aspectsof transport and compartmentation in eukaryotic cells, are of paramountimportance.Antibiotics are natural products of microbial origin. However, these arenaturally produced only in minute quantities that are not even detectable innature. Overproducing individuals are present in nature and screening largepopulations can always yield better producers. Appropriate modifications toculture medium and culture conditions also result in higher production.Generating mutants artificially and screening increase the chances of findingsuch overproducers. A big leap in this direction was possible due to the newbiotechnological tools such as genetic engineering. This possibility wasalready under consideration for more than two decades (Chater, 1990). Therehad been a slow progress as antibiotic synthesis occurs as a combination ofthe action of several genes.While antibiotics are extremely useful in medicine and veterinary medicine,the development of resistance by the target pathogens is an increasingproblem. Therefore heavy investments are made into research leading to thediscovery of new antibiotics. However, the natural antibiotics belong to a fewfamilies and it may not be possible to isolate new and therapeuticallyimportant antibiotics belonging to new families. Once resistance is developedit is possible this resistance extends easily for that particular family ofantibiotics. Therefore the modification of already known antibiotics to generatesemisynthetic antibiotics, either chemically or enzymatically, may bemore appealing.