Heterologous expression of the glucose oxidase gene in Trichoderma atroviride leads enhanced ability to attack phytopathogenic fungi and induction of plant systemic disease resistance

A transgenic strain of Trichoderma atroviride that expresses the Aspergillus niger glucose oxidase gene goxA under a homologous pathogen-inducible promoter (nag1) has been constructed, with the aim of increasing the ability of this biocontrol agent (BCA) to attack phytopathogenic fungi and enhance plant systemic disease resistance. The sporulation and growth rate of the transgenic progenies were similar to the wild-type strain P1. goxA expression occurred immediately after contact with the plant pathogen, and the glucose oxidase formed was secreted extracellularly. The transformed strain SJ3 4, containing 12-14 copies of the transgene, produced significantly less N-acetyl-glucosaminidase and endochitinase then wild type. However, the ability of its culture filtrate to inhibit the germination of Botrytis cinerea spores was increased by about 3-fold. In comparison to P1, the transgenic strain more quickly overgrew and lysed in vitro the pathogens Rhizoctonia solani and Pythium ultimum. In assays in vivo SJ3 4 showed a highly improved biocontrol ability in soil heavily infested with those pathogens, where the wild type was unable to protect the plant and allow seeds to germinate. The Trichoderma-gox was able to induce a much higher level of systemic resistance against the foliar pathogen B. cinerea, as compared to the parent strain. This work demonstrate that i) heterologous genes driven by pathogen-inducible promoters can improve the biocontrol and Induced Systemic Resistance properties of fungal BCAs such as Trichoderma spp., and ii) these microbes can be used as vectors to provide the plant with useful molecules able, for instance, to increase pathogen