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Structure and function of seed microbiomes from 98 plant species

Posy Busby: Oregon State University

<div>Seeds are the organs of generational and genetic renewal and recombination in plants, yet we lack a unified view of the seed microbiome that includes both mutualists and pathogens, and more plants than just crops and a few models. We characterized culturable endophytes from 98 plant species from 39 families (70 seed samples per plant species, pooled from many plants per species), and then tested interactions between seed endophytes and pathogens in <em>Triticum aestivum</em> (winter wheat). Overall, 65.6% of all surface-sterilized seeds lacked isolates on PDA; 30.6% were characterized by a single, primary symbiont of varying identity. Less than 4% of seeds overall hosted two or more culturable endophytes. Despite sampling 16 orders of plants, primary symbionts were dominated by fungi in a single order, Pleosporales. In winter wheat, seed endophytes reduced the severity of leaf rust disease caused by <em>Puccinia triticina</em>, with effects stronger in five-year-old seed compared to one-year-old seed. Our results support a simplified seed microbiome that contrasts strongly to the taxonomically diverse vegetative microbiomes of land plants. However, disease modification appears to be function common to endophytes found in seeds, roots, shoots and leaves.</div>