Unraveling the mechanisms by which novel fungal-plant associations evolve

University Of Maryland, College Park, College Park MD

Investigators

Abstract

Elucidating the connection between genotype and adaptation is fundamental to the study of evolutionary biology, yet it remains an elusive goal. A minority of strains of the insect pathogenic Metarhizium robertsii (Mr) are root colonizing plant growth promoters. This project will examine the mechanisms by which novel symbioses can rapidly emerge using comparative and evolutionary approaches that integrate a genetic screen with a transcriptional profiles of strains showing a spectrum of mutualistic associations. Rapid evolution is a trait shared with pathogens, pests and cancers; although in most cases the underlying mechanisms are poorly understood. Addressing these mechanisms with Mr, which is an experimentally very tractable model system, will involve asking many basic questions on poorly understood topics that span much of molecular evolution, such as the relative importance of amino-acid versus regulatory evolution. Moreover, understanding ecological diversification is particularly crucial for predicting the outcome of fungal responses to climate change and disease outbreaks. By focusing on the genetic basis of recent adaptive changes this project will address the uncertainty of how invasive strains could interplay with the biological world and adapt to a new natural environment. Metarhizium fungi are already deployed as biological insecticides, and by identifying how they work as plant symbionts, and when and why they do not, this work will facilitate their use in an expanded role as comprehensive plant growth promoters. As Metarhizium fungi are closely related to many important plant pathogens and biocontrol fungi, the results and conclusions from this work will have many applications. The unusually broad array of ecological niches exploited by Mr allows a genes function to be accessed in all these lifestyles, while the spectrum of endophytic associations in Mr populations provide a model where genomic variation can be related to adaptation to particular lifestyles. By focusing on the genetic basis of recent adaptive changes this project will address the uncertainty of how invasive strains could interplay with the biological world and adapt to a new natural environment. Identifying the factors that contribute to plant associations will be achieved by comparative and evolutionary approaches that integrate transcriptional profiles of strains showing a spectrum of mutualistic associations with a genetic screen of a growth promoting strain. These complementary methodologies will test the hypothesis that rapid changes in plant associations are determined by regulatory controls of gene expression. This proposal will also clarify central "unknowns" such as whether there are large sets of effector proteins, whether they have overlapping functions with the pathogenic insect interaction or whether Mr has a more limited repertoire of key effectors that are deployed to colonize plants. Additional experiments will characterize these effectors and their promoters to further address the underlying regulatory, metabolic and biosynthetic differences that define symbiotic associations. Collectively, these experiments will address fundamental questions on how environmental interactions shape organismal and genome diversity, as well as the capacity of Metarhizium fungi to rapidly evolve and adapt to new habitats. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.