This project focuses on a protein called Cdc14. The protein was described initially as a regulator of the replication of nuclei during cell growth, and is generally assumed to play that role in most organisms. However, recent findings conflict with that traditional model. This research will bring a new perspective to the Cdc14 story by examining Phytophthora infestans, a plant pathogenic microbe that was the cause of the historic Irish Famine of the mid-1800's and is still a major threat to food production. P. infestans grows by forming hyphae that make stationary spores that in turn release swimming spores. Its Cdc14 is needed to form the swimming spores, and much of the protein localizes to the swimming apparatus, also known as flagella. To learn more about the function of Cdc14, experiments will be performed to define precisely where in the cell the protein resides, learn how it is targeted to those locations, test how it influences swimming spore behavior, and study proteins that may be regulated by Cdc14. This work will contribute to the development of a unified theme to explain the function(s) of Cdc14 in P. infestans and other species. It will likely also be relevant to understanding the formation and evolution of flagella, which are central to the life cycles of both single-cell and multicellular organisms. Broader impacts
Phytophthora and its relatives cause numerous destructive diseases on plants and animals in agriculture and natural environments. The research may lead to ways to prevent losses in those systems, for example by identifying cellular targets that if inhibited would block infection of hosts. The work also integrates research, education, and outreach, as it will train a postdoctoral fellow, graduate students, and undergraduates. The investigator has a record of supporting undergraduate research by students from under-represented groups, and providing the oomycete research community with experimental tools and training. Such activities will continue throughout this project.
The broad objective of this project was to learn what regulates sporulation and spore behavior in the plant pathogen Phytophthora infestans, which causes the devastating late blight diseases of potato and tomato. Spores are an important life-stage since they move pathogens plant-to-plant, and generate the infection structures used to initiate disease. We discovered that light and humidity regulate formation of P. infestans spores, and identified transcription factor proteins that turn on the genes needed to form spores. The binding sites in DNA for transcription factors that regulate spore formation, spore germination, and the infection stages were also identified though a combination of functional testing and experimental validation. We also characterized the proteins that comprise the flagella of P. infestans, which the spores use to swim towards infection sites on a host. One protein, Cdc14, was of particular interest since it was not previously thought to be flagella-associated in other eukaryotes, and by silencing its gene we showed that it is essential for spore formation. We also identified transcription factors that are needed to express Cdc14 and studied how the protein moves from nuclei to flagella at different stages of the life cycle. This involved identifying the parts of Cdc14 that are needed for targeting it to the different organelles. We discovered that nuclear localization signals from oomycetes such as P. infestans do not conform to the definition identified in studies of traditional model systems. Several transcription factors that have expression patterns similar to that of Cdc14 were also shown important for protecting spores and hyphae from oxidative stress damage, such as would be encountered during plant infection. Broader impacts of this work include training two postdoctoral researchers, four graduate students, and two undergraduates; the latter are first-generation college students and underrepresented minorities, both of which are now attending graduate school in STEM fields. Studying the biology of pathogen spores also has the potential of broad impact, since the sporulation pathway can be targeted by chemical inhibitors to help control disease and ensure global food security.