Dynamic mini-chromosomes: mechanisms of exchange, stability and causation of fungal pathogen adaptation

点击翻译按钮获取中文摘要

Food crops are constantly threatened by new variants of established pathogens and by newly-emerged pathogens. The rice blast fungus Magnaporthe oryzae has a long history of variation to overcome resistance deployed in rice crops, and a new M. oryzae variant emerged in 1985 to cause devastating disease on wheat in Brazil. Wheat blast disease is proving even harder to control than rice blast because potential resistance genes identified using strains from the 1980s are no longer effective in controlling recent aggressive isolates. Global spread of the disease and lack of control measures enhance fears about global food security. Recent studies indicated that dispensable supernumerary chromosomes from blast field isolates might accelerate adaptive evolution and contribute to virulence of the fungus. Supernumerary chromosomes are hypothesized to play roles in the evolution of pathogen genes that are critical for resistance in host plants, including host specificity at the plant species/genus and the crop cultivar levels. The project will study supernumerary chromosomes to understand their prevalence, movement between strains, DNA exchange with core-chromosomes, stability, and contributions to pathogenicity and virulence. Outcomes will be valuable for understanding genomic dynamics of the blast pathogen and help reveal roles of supernumerary chromosomes in many plants, animals and other fungi. Graduate students and undergraduates will receive broad training in genomics, bioinformatics, molecular plant-microbe interactions, and plant biosecurity. Undergraduates will participate in an 8-week summer research experience in plant disease diagnostics involving collections in the field and identification of disease organisms using cutting edge sequencing technologies. The fungus Magnaporthe oryzae causes blast diseases on more than 50 grass species, which include the ancient rice blast and the newly emerged wheat blast. Global agricultural threats posed by blast diseases and evolving pathogens make it important to understand genome dynamics of blast pathogens. The blast fungal genome includes hundreds of putative effector genes that are specifically expressed during host invasion and that generally encode small secreted proteins involved promoting disease. A subset of these effectors is recognized by host resistance gene products, which triggers resistance and blocks infection of that host. Such effectors play a major role in determining host specificity in blast fungal pathogens, both at the host species/genus level, and at the crop cultivar level. The recent genomic data of dispensable supernumerary chromosomes from the wheat blast field isolates showed that the supernumerary chromosomes contain many effector genes that are often found on indispensable core-chromosomes in other strains, as well as other genes that may play a role in pathogen aggressiveness. This project proposes to further understand supernumerary chromosomes with respect to their prevalence, inter-strain movement, DNA exchange with core-chromosomes, stability, and contributions to pathogenicity and virulence. The hypothesis will be tested that supernumerary chromosomes play roles in effector mobility by serving as a repository for effector genes that are deleted from core-chromosomes, and a role in mediating their relocation on core-chromosomes. The project will combine methodologies in blast disease biology, including adaptive evolution strategies, parasexual transfer between fungal strains, molecular biology, genomics, and cytology.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.