Becoming a fungus: comparative phylogenomic studies of evolution of hyphal growth and absorptive nutrition in fungi

点击翻译按钮获取中文摘要

Fungi can cause plant diseases, serve as mycorrhizal partners, and decompose litter and woody debris, all because of the tubular hyphae (filaments of cells, surrounded by a cell wall) that make up their bodies. Hyphae poke and penetrate into substrates while secreting digestive enzymes across their complex cell walls. The enzymes digest organic compounds into simple, diffusible molecules, which fungi absorb to fuel their growth, making fungi the most important terrestrial eukaryotic saprotrophs. However, phylogenetic evidence shows fungi and animals share a common ancestor and the earliest fungi were unicellular not hyphal; wall-less and probably phagotrophic instead of ingesting nutrients across a cell wall; and aquatic and with a flagellated stage rather than terrestrial. Reconstructing evolution of hyphal construction, secreted digestive enzymes, and terrestrial growth, are main themes of the proposed research. We will take advantage of seven new genome sequences for early-diverging fungi, the result of our successful community sequencing proposal to the US Joint Genome Institute. We will test whether ancestral fungi were unicellular or hyphal based on patterns in phylogenetic trees. We will compare the well-studied genes for hyphal growth from Ascomycota with those of early-diverging fungi where they have never been analyzed. Combining the genomic sequences with the new data from additional fungal groups, we will use phylogenetic analysis of conserved genes for digesting plant materials such as cellulose or for digesting animal tissue to infer when and where the ability to breakdown plant products evolved in the fungi. This analysis has the potential to reveal new groups of enzymes with industrial applications. Combining my continuing interest in the Ascomycota and molecular clocks, we will also analyze the record of dispersed fungal spore fossils to help establish minimum ages of important diversifications. This research will contribute to training ~4 Ph.D. students to apply methods of molecular biology to questions of broad interest in fungal evolutionary biology.