Pathogens can decimate crop plants and are a major threat to food security. Understanding how plants and microbes interact will help researchers develop tools and resources to avoid crop damage and reduce the spread of disease from pathogens. Recently, scientists have discovered microscopic bodies in the spaces between plant cells, and these so-called extracellular vesicles (EVs) are thought to play a role in signaling between microbes and host plants. Although well studied in animals, how EVs function in plants is not fully understood. To understand their function, new biochemical techniques were developed and it was found, surprisingly, that EVs contain "stress response" proteins, and carry small molecules (sRNA), which are known to shut down (or silence) genes. The project tests the hypothesis that plant EVs may carry and transfer these important sRNA signaling molecules between microbes and plant hosts. The team will also study how plant EVs are produced, and how plants and pathogens exchange EVs. The outcomes of the research will provide key knowledge to improve plant disease resistance, with long-term practical outcomes for society. Notably, controlling disease spread will improve food security while reducing production costs and use of environmentally harmful fungicides. Understanding the role of EVs could yield targets for engineering resistance to pathogens and will advance analytical methods for studying how molecules are transferred between host plant and pathogen. Educational impacts will be achieved through interdisciplinary training of students and post-doctoral scientists in the area of plant - microbe interactions and in computational biology. <br/><br/><br/>This project will focus specifically on EVs from Arabidopsis, plus a model legume, Medicago truncatula (a relative of alfalfa), with pathogen analyses focused on Colletotrichum, a genus of fungi that include many highly destructive species, and Phytophthora, a genus of oomycetes that includes P. infestans, the causal agent of the Irish potato famine. The work will be done in these species because there are significant, existing genetic and molecular resources and background work, including from the European partners of the project. The questions to be addressed by this project include whether EVs are a primary mechanism for transfer of information between plants and their fungal pathogens? What are the contents of the EVs? How are the EVs transferred and delivered? Ultimately, the project will address whether altering the contents of the EVs has a significant impact on plant-fungal interactions. The project will characterize phenotypes of plants and potentially fungal and oomycete strains altered in their EV contents. Project members will be trained broadly in plant and fungal interactions, small RNA biology and genomics, cell biology and microscopy, and computational methods through individual and group projects in the analysis of the localization, biogenesis, and biochemistry of EVs. The results will have broad impact though interdisciplinary training and will promote national security by contributing basic knowledge to improve plant disease resistance.<br/><br/>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.