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Population biology and comparative genomics of Claviceps purpurea and other defensive mutualists in the Hypocreales

Kirk Broders: Colorado State University

<div>The genus <em>Claviceps</em> includes many species that are ovarian parasites of Poaceae, causing the disease ergot resulting in the production of sclerotia in place of seeds. The genus recently experienced advances in the delimitation of cryptic species and separate lineages with respect to geographic distribution and host preference. It was also recently discovered that <em>C. purpurea </em>produces both cytokinins and auxins during infection. Current outbreaks of ergot on barley in relatively geographically isolated areas has spurred efforts to analyze the population structure, study the evolution of phytohormone production in agriculturally important <em>C. purepurea</em>, and examine effects of infection on the host. A phylogenetic analysis of five housekeeping gene loci demonstrated that <em>C. purpruea</em> isolates from the U.S. were distinct from European isolates, but no subpopulations in relation to host preference were observed. A comparative genomic analysis of over 115 species within the Hypocreales revealed orthologs of <em>C. purpurea </em>cytokinin biosynthesis genes and putative auxin genes in members of the closely related tribe Balansiae, which contains beneficial fungal endophytes. Together these results indicate a distinct population of <em>C. purpurea </em>infecting barley and other grasses in the central plains, and the evolution of phytohormones may play an important role in the ecology and evolution of <em>Claviceps </em>and other species in the Hypocreales as defensive mutualists with a broad host range.</div>