Introduction of heterologous genes

Most research on engineered strains has focused on adding new biocontrol genes into known BCAs of pathogens, insects and weeds. For example, Trichoderma atroviride P1 suppresses a wide range of foliar and soilborne pathogens. Insertion of the Aspergillus niger glucose oxidase-encoding gene (goxA) under the control of the homologous chitinase (nag1) promotor into strain P1 yielded the transgenic strain SJ3-4 (containing 12-14 goxA copies) that induced systemic resistance against Botrytis cinerea and controlled Pythium ultimum and Rhizoctonea solani on bean better than did P1 (Brunner et al., 2005).

Bacillus thuringiensis cry genes have been introduced into a wide variety of bacteria (e.g. Pseudomonas fluorescens, Agrobacterium radiobacter, Ancylobacter aquaticus, Clivibacter xyli and Herbaspirillum seropedicae). These transgenic strains inhibited a variety of pests, including tobacco hornworm (Manduca sexta), malaria mosquito (Anopheles stephensi), leather] acket (Tipula oleraceae) and European corn borer (Ostrinia nubilalis) (Downing et al., 2000; Obukowicz et al., 1986a, 1986b; Yap et al., 1994). Bacillus transformed with the mosquitocidal Cry and Cyt proteins of Bacillus thuringiensis and the binary toxin of Bacillus sphaericus showed 10-fold better efficacy against Culex spp. (Federici et al., 2003).

In another line of research, Metarhizium anisopliae ARSEF 549 was engineered to express the insect-specific neurotoxin AaIT from the scorpion (Androctonus australis). Toxicity of the transgenic strain increased 22-fold against tobacco hornworm (Manduca sexta) catepillars and nine-fold against adult yellow fever mosquitoes (Aedes aegypti) (Wang and St. Leger, 2007).

Most interesting was the report by Fang et al. (2011) who engineered Metarhizium anisopliae to produce and deliver molecules that selectively block the development of the causal agent of malaria (Plasmodium falciparum) in the mosquito.

A final example relates to biocontrol of weeds. Introduction of NEP1 (encodes a phytotoxic protein from Fusarium) into Colletotrichum coccodes increased nine-fold the virulence of the fungus on the herbicide-resistant weed velvetleaf (Abutilon theophrasti).

The transgenic strain killed more rapidly and at a lower dose that the wild-type strain (Amsellem et al., 2002).

 
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