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Friday, November 1, 2019 at 12:20pm
Graduate Student Exit Seminar, Raguso Lab, Plant Biology, Cornell University
Nearly all eukaryotes form close relationships and interactions with microbes that are essential for their health and fitness. The presence of microbes on and within plant tissues is ubiquitous and accordingly, the observed phenotype of most plants is a combination of genes expressed by both plants and microbes. Considering this, microbially derived traits may be overlooked or mistaken for plant derived traits due to the limits and biases of our perception and investigation. In particular, some aspects of floral mimicry, including brood-site deceptive floral scents that mimic fermenting fruit, carrion, or feces, show the chemical signatures of microbial metabolism but have not been investigated to determine if they are of plant or microbial origin. A particularly striking example is the common pawpaw Asimina triloba (Annonaceae), a small understory tree native to the deciduous forests of eastern North America. These clonal patches of trees produce an early spring bloom of small, maroon colored flowers with a floral scent that is strongly reminiscent of fermenting fruit or bread dough. Not surprisingly, the floral scent of A. triloba is dominated by aliphatic fermentation products including ethanol, ethyl acetate, 3-methyl-1 butanol, acetoin, and acetic acid and consequently attracts sap beetles (Nitidulidae) and Drosophilid flies that are deceived while searching for oviposition/mating sites. It remains unclear how these floral traits have evolved, or whether the flowers have outsourced this function to third-party agents (microbes) to circumvent the microevolutionary processes required to evolve this phenotype. To test this hypothesis, we investigated the microbiome of A. triloba whole flowers, as well as the change in microbial community during protogynous floral ontogeny and between distinct spatial units of the flower, using both culture independent and classic microbiological methods. In addition, we performed manipulative experiments including flower sterilization, exclusion of biotic microbial vectors via micromesh bagging, electroantennographic examination of pollinator sensory capabilities, and insect trap bioassays in the field to test the hypothesis of microbial-mediated signaling between A. triloba flowers and their pollinators. Our results document unexpected diversity and abundance of fungi and bacteria inhabiting the flowers, as well as spatio-temporal patterns of microbial community composition during the flowers’ short lifespan. Additionally, our manipulative experiments have revealed candidate microbially produced volatiles, and our bioassays suggest that microbes on A. triloba flowers affect the attraction of Nitidulid beetles in the field.