INFLUENCE OF THE PRODUCTION OF ANTIBACTERIAL AND ANTIFUNGAL PROTEINS BY TRANSGENIC PLANTS ON THE SAPROPHYTIC SOIL MICROFLORA

To obtain durable and broad-spectrum resistance against plant pathogen s, plants are transformed with genes coding for antimicrobial proteins from plant, animal or microbial origin. An obvious concern is that in creased levels of these antimicrobial compounds affect not only the ta rget pathogen, but also beneficial micro-organisms such as mycorrhizae , rhizobia and other micro-organisms involved in plant health, litter decomposition and nutrient cycling. This literature study focuses on e ffects of these transgenic plants on the non-target saprophytic soil m icroflora. Transgenic plants that constitutively express proteins with potential antifungal and/or antibacterial activity, can reduce activi ties of specific soil-borne plant pathogens in the rhizosphere. Report s on non-target effects on the saprophytic soil microflora are scarce and incomplete, and mainly focused on mycorrhizal symbiosis. Constitut ive expression of antifungal pathogenesis-related proteins in tobacco in most cases did not affect root colonization by the mycorrhizal fung us Glomus mosseae. However, increased levels of a class II tobacco bet a-1,3-glucanase reduced the colonization potential, indicating that no n-target effects can occur. Concerning other members of the plant-bene ficial rhizosphere microflora, it can be assumed that they will come i nto contact with the transgenic product. By natural wounding, senescen ce and sloughing-off of root cells, at le!ast some of the antimicrobia l protein(s) will be released in the rhizosphere. Despite proteolytic activity of the rhizosphere microflora, part of the protein can remain active due to protective adsorption to clay minerals or humic compone nts.