CAREER: Investigating the mechanistic basis of host adaptation in close and distant relatives within Xanthomonas species complex

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Increased global trade, modern agricultural practices and global climate change have predisposed agro-ecosystems to the increased risk of outbreaks of old and new diseases. These outbreaks impacting food security are a major societal concern. To manage disease outbreaks, understanding various mechanisms employed by diverse pathogenic species to infect a common host or, at times, to acquire infectivity on a new host is crucial. While molecular mechanisms underlying pathogenesis on a given host have been uncovered in individual pathogenic species, understanding whether these mechanisms are conserved across diverse species infecting common host remains elusive. The goals of this project are to 1) understand various mechanisms that diverse pathogenic bacteria use to specialize on a common host, 2) identify traits that allow pathogenic bacteria to acquire infectivity on a new host. This knowledge will help resolve complex interactions between plants and pathogens and foster development of effective strategies to respond and manage pathogen populations. The educational goals include fostering STEM research interests by providing research opportunities for high-school students from high-need schools in Alabama and first-generation minority undergraduate students, and raising public knowledge of emergence of plant disease outbreaks, their influence on plant health and, ultimately, on our lives. The project will educate students on what makes bacterium pathogenic and how diseases emerge in the modern era of agriculture. Conceptualizing host range of plant pathogenic bacteria has been a challenge. Population genomics, association analyses, and transcriptomics approaches have proposed a new paradigm stating host range as an overlapping genetic continuum involving multiple genetic determinants with small to major effect. However, functional validation of the select candidates has not been sufficient to uncover the basis of host range. Using Xanthomonas species complex as a model system where both pathological convergence as well as recent host range expansion have been observed, the project will test the idea that host range determinants are not restricted to the pathogenic phase, but asymptomatic early phase is equally important in determining overall dynamics of essential pathogenicity determinants. Deploying forward and reverse bacterial genetics, pathogen transcriptomics, experimental evolution and high-throughput sequencing tools, the project will test the following hypotheses; i) functionally conserved essential determinants from diverse pathogen species are involved in the infection of a common host causing the same disease, although their temporal dynamics may vary depending on contribution of other variable fitness determinants; ii) genetic exchange of adaptive traits in closely related species under host selection pressure and in presence of competing species is responsible for host range expansion. The project will identify genetic determinants during infection process that govern qualitative and quantitative differences across different pathogenic species. Understanding of the fitness adaptations that explain emergence of novel pathogen lineages will reveal pathogen weaknesses. This project will advance the knowledge of genetic mechanisms and their functional significance underlying host adaptation in modern agriculture.This project is jointly funded by IOS-Plant Biotic Interaction and the Established Program to Stimulate Competitive Research (EPSCoR).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.