Bee Pollination Modifies the Structure of the Seed Microbiota

To date, little is known about the assembly of the seed microbiota. Some early microbial seed colonizers are transmitted from the maternal plant to the seed through the vascular system while other enter through the stigma. Thus, the seed microbiota, consists of microbes not only recruited from the vascular tissues of the plant, but also from the flower. Flowers are known to be a hub for microbial transmission between plants and insects. This floral-insect exchange opens the possibility for insect-transmitted bacteria to colonize the ovule and subsequently the seed, and to pass then into the next plant generation. In this study, we evaluated the contribution of insect pollination to the seed microbiome through 16S rRNA amplicon sequencing. Brassica napus flowers were subjected to Apis and Osmia bee pollination, hand pollination or autonomous self pollination (ASP). Sequence analyses revealed that Apis pollination reduced the bacterial richness and diversity, increased the beta diversity amongst plants and introduced bee associated taxa. In contrast, Osmia pollination had minor effects on the seed microbiome. Insect pollination is therefore an ecological process involved in the transmission of bacteria from flower to seeds.