Plant-fungal communication: using an endophytic insect pathogenic fungus as a model

点击翻译按钮获取中文摘要

The commercially important insect pathogenic fungus, Metarhizium robertsii (= anisopliae) has a world-wide distribution and can be easily recovered from soils of different climates and ecological settings such as forested or agricultural habitats. My laboratory has shown that Metarhizium spp. are not only insect pathogens but also endophytes, with evidence that they can adhere to plant roots and colonize root cells. We have connected the lifestyles of Metarhizium as insect pathogens as well as endophytes and have shown that the relationship of this fungus is beneficial to the plant. We have shown that fungal mycelia from infected insects migrate to plant roots that are then colonized. Subsequently the insect-derived nitrogen is transferred to the plant. We hypothesize that this is a symbiotic association where insect nitrogen is provided to the plant by the fungus in exchange for plant carbon (i.e. carbohydrates). Elucidating the association of this fungus with plants could generate alternate ideas of nutrient cycling in plants, particularly nitrogen cycling. This fungal-insect-plant association could also contribute to the utility of fungi as insect pathogens particularly for insect pests that destroy plant roots. For example, in North America there are over 120 root feeding insects and in Canada insects that destroy plant roots include strawberry root weevil (Otiorhynchus ovatus), black vine weevil (O. sulcatus), several species of wireworms and cutworms (Euxoa spp.), Grape Root Borer (Vitacea polistiformis) and several forest root feeding insects. My next progression in the research program, which is described in this proposal, is to understand at a greater depth, the association of this insect pathogenic fungus with the plant. The overall objective of this proposal is to increase our understanding of the association of endophytic insect pathogenic fungi with host plants and the mechanisms that allow these associations. We will endeavor to test the following hypotheses: Hypothesis 1: That the plant reciprocates fungal nitrogen transfer with carbon transfer. Hypothesis 2: That soil nitrogen levels affect endophytic association by M. robertsii. Hypothesis 3: That there is plant-fungus communication that accomodates endophytic colonization. Hypothesis 4: That M. anisopliae protects plants from a large array of plant pathogenic fungi, root as well as systemic pathogens.