How to Drive the Transmission of Seed Bacterial Communities to Seedling

Seeds represent the starting point of plant microbiota assembly, which includes commensals, pathogens and beneficial microbes. The seed is therefore a key vector organ for plant health and protection. However, harnessing beneficial plant-microbiota interactions requires exploring and understanding the processes involved in microbiota assembly on seeds and its modifications during germination and plant emergence. A prerequisite was to describe the importance of seed microbiota in a large-scale meta-analysis across 50 plant species that shows a core microbiota composed of 30 microbial taxa and a very diverse flexible microbiota (Simonin et al. 2022). However, our results suggest that the most abundant seed microorganisms are not necessarily the ones that have the highest transmission success to seedlings. Our studies on bean, radish and rapeseed show that plants first recruit rare bacterial taxa from soil and seed (Rochefort et al 2019, Chesneau 2022). To better understand the transmission and effects of seed-borne taxa, we then performed inoculations of seed-borne bacterial synthetic communities (SynComs) on seeds. These experiments demonstrated a phylogenetic signal associated with the transmission success of strains from seeds to seedlings and the important role of mass effects. Additionally, we observed a strong influence of the composition of the initial SynCom on transmission success due to biotic interactions. SynCom inoculations also led to a modulation of various plant phenotypes, including emergence rates, seedling development and impact of a soil-borne pathogenic fungus. Altogether, we present evidence of the feasibility and potential of plant microbiota engineering using seed-borne bacterial SynComs inoculated on seeds.