MICROBIAL GENES EXPRESSED IN TRANSGENIC PLANTS TO IMPROVE DISEASE RESISTANCE

Abstract

The development of plant transformation and gene cloning techniques has opened new avenues for augmenting disease and insect resistance in crops. The concept of ‘Genetically Acquired Resistance’ now encompasses a variety of strategies based on the transgenic expression in plant of genes from many different origins. Some of the most potentially useful transgenes capable of enhancing resistance to attack by microbes, viruses and insects have been obtained from bacteria and fungi, which are regarded as rich sources of desirable traits for plant genetic improvement. The main research directions have included: (i) the enhancement of the plant anti-microbial and insecticidal arsenal by the constitutive or inducible synthesis of various pathogen inhibiting compounds; (ii) the alteration of the plant response to pathogens by the appropriate induction of the local or systemic defence mechanisms, or by the interference with plant-pathogen signalling and (iii) the inactivation of pathogen toxins or the improvement of plant resistance to them. Although transgenic plants that are insect- resistant or bear other useful traits obtained from microbes, such as herbicide-resistance or enhanced food quality, are being commercially marketed, genetically- engineered crops exhibiting resistance to fungal or bacterial diseases have yet to reach the marketplace. The main focus of this paper addresses the application of bacterial or fungal genes to improve plant resistance to insect, fungi, bacteria and viruses, and the usefulness of these microbial genomes in the development of new transgenic technologies. In addition, perspectives dealing with environmental concerns and important biosafety questions resulting from these technologies are briefly discussed.