Metabolic and microbial interactions in the spermosphere of germinating common bean seeds

The spermosphere, which is the dynamic interface surrounding germinating seeds, constitutes a key environment influencing plant health and vigor (Nelson, 2004; Schltz et al., 2015). It is shaped by the complex interaction between compounds exuded by seeds, derived from both primary and specialized metabolism, and the microbial communities that colonize it. Shortly after imbibition, these interactions determine the success of seedling emergence and their ability to withstand climatic, nutritional and biotic stresses. Yet the influence of genotype and production conditions on these interactions remains largely under-studied. The chemical and microbial diversity of the spermosphere also remains largely unknown.

A comprehensive analysis was conducted on eight common bean (Phaseolus vulgaris L.) genotypes from two contrasting production regions, combining metabolomics and microbial metabarcoding. Among the 2,467 metabolites detected, amino acids, flavonoids and terpenes were predominant. In parallel, 19 bacterial families and 23 fungal families were identified, with their composition varying according to genotype and production environment. Integrated metabolome–microbiome analysis revealed specific associations, including a negative correlation between Bacillus spp. and certain flavonoids. Thus, seeds, through genotype-dependent differences in their exudates, actively shape their microenvironment. These findings highlight the decisive role of genotype in the chemical and microbial regulation of the spermosphere and provide deeper insight into the early mechanisms underpinning germination and plant development.

This work opens up new perspectives for enhancing seed vigour and improving crop resilience to environmental stress.

The research advances the use of plant functional diversity to optimise metabolic traits that contribute to crop quality. By closely characterising exudate–microbe interactions, it identifies levers for selecting genotypes that combine high-quality plant products with the capacity to shape a beneficial microbiome from the moment seeds germinate.
A deeper understanding of these early interactions between seeds, molecules and the microbiota will support the development of innovative strategies to reduce pesticide use.

References
Nelson, E. B. (2004). Microbial dynamics and interactions in the spermosphere. Annu. Rev. Phytopathol., 42(1), 271-309.
Schiltz S, Gaillard I, Pawlicki-Jullian N, Thiombiano B, Mesnard F, Gontier E. 2015. A review: what is the spermosphere and how can it be studied? J Appl Microbiol 119:1467–1481.


Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences in collaboration.