Insect pathogenic fungi and the plant rhizosphere

绿僵菌是一种具有重要商业价值的子囊菌类昆虫病原真菌，分布极为广泛，可以很容易地从不同气候和生态环境的土壤中恢复，例如森林或农业生境(Roberts&St.Leger，2004)。最近，金龟子绿僵菌被证明具有植物根际能力，有证据表明它可以附着和定植植物根部，这表明它在植物根际具有另一种作用。当绿僵菌在豆根分泌物存在的情况下生长时，它会上调特定的基因亚集。其中最好的研究是MAD2，它编码一种植物粘附素。在昆虫角质层存在的情况下，它会上调另一组不同的基因，包括编码昆虫角质层粘附素的Mad1。这种真菌似乎至少有一种两用的生活方式。这项建议的目的是进一步调查这种昆虫病原真菌与植物根的关系。作为根际真菌，它有哪些类型的联想？金龟子绿僵菌的不同基因型别是否表现出与不同植物物种形成联系的不同能力？这是一种互惠互利的关系吗？真菌向植物提供昆虫氮，以换取碳？金龟子绿僵菌能保护植物免受食根性昆虫的侵害吗？这一建议代表了对这些真菌在土壤生态系统中所起作用的更广泛理解的转变，特别是它们在植物根际所起的作用。阐明这种真菌与植物的关系可以产生关于植物营养循环的另一种想法，特别是氮循环。这种真菌-昆虫-植物组合也有助于利用真菌作为昆虫病原体，特别是对破坏植物根部的害虫。这项建议的总体目标是增加我们对昆虫病原真菌与寄主植物之间的联系以及这些联系的机制的了解。这是一个特别新颖的建议，因为它研究了真菌-昆虫-植物的三方相互作用，这可能具有重要意义，因为某些昆虫病原真菌可能在植物保护中发挥作用。

The commercially important ascomycetous insect pathogenic fungus, Metarhizium anisopliae has an extremely wide distribution and can be easily recovered from soils of different climates and ecological settings such as forested or agricultural habitats (Roberts & St. Leger, 2004). Recently, M. anisopliae has been shown to be plant rhizosphere competent, with evidence that it can adhere to, and colonize, plant roots strongly suggesting an alternate role in the plant rhizosphere. M. anisopliae upregulates a specific subset of genes when grown in the presence of bean root exudate. The best studies of these is Mad2, which encodes a plant adhesin. In the presence of insect cuticle it upregulates a different subset of genes, including Mad1, which encodes for an insect cuticle adhesin. This fungus appears to have, at least, a bifunctional lifestyle. The objective of this proposal is to further investigate the association of this insect pathogenic fungus with plant roots. What types of associations does it have as a rhizoplane fungus? Do different genotypes of M. anisopliae show differing abilities to form associations with different plant species? Is this a mutualistic association where the fungus provides insect nitrogen to the plant in exchange for carbon? Does M. anisopliae afford plant protection from root feeding insects? This proposal represents a shift in the wider understanding of the role these fungi play in the soil ecosystem, particularly the role they play in the plant rhizosphere. 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. The overall objective of this proposal is to increase our understanding of the association of insect pathogenic fungi with host plants and the mechanisms of these associations. This is a particularly novel proposal since it investigates the tripartite interaction of fungus-insect-plant, which could be of significance since certain insect pathogenic fungi could have a role in plant protection.