Bacterial succession during seed development

Seed microbiota acts as a starting point for the assembly of the plant microbiota and contributes to successful plant establishment. To date, the order and timing of microbial taxa immigration during seed development and maturation remained unknown. We investigated the temporal dynamics of seed-associated bacterial assemblages in two plant species, common bean (Phaseolus vulgaris) and radish (Raphanus sativus). Structure of bacterial assemblages associated to buds, flowers, fruits and seeds collected during seed filling and maturation were estimated through amplicon sequencing. Comparative genomic analyses of bacterial populations specifically associated to floral and seed habitats were performed to identify genetic determinants involved in seed transmission. While phylogenetic diversity of seed bacterial assemblages was similar for both plant species during seed development, higher heterogeneity in assemblage structure was observed for radish. This higher dispersion was in part due to floral-transmitted taxa, which were not detected in bean, consistent with their different pollination modes. Investigation of genetic determinants involved in seed transmission revealed some potential candidates in the dominant bacterial species associated to bean. This study provided a first glimpse on processes involved in seed microbiota assembly and acted as a first step towards the design of plant-beneficial microbial consortia that could be incorporated within seed.