Global architecture of metabolite distributions across species and its formation mechanisms

Living organisms produce metabolites of many types via metabolic reactions. Especially, flavonoids, a type of secondary metabolite, of plant species are interesting examples. Since plant species are believed to have specific flavonoids that were formed response to diverse environments, elucidation of the design principles of metabolite distributions across plant species is important for understanding metabolite diversity and plant evolution. In our previous study, we found heterogeneous connectivity in metabolite distribution, and proposed a simple model to explain the possible origin of heterogeneous connectivity. In this paper, we determine additional structural properties of metabolite distribution among families that are analogous analogy with plant–animal mutualistic networks: nested structure and modular structure. An earlier model representative of these structural properties in bipartite relationships was established on the basis of the traits of elements and external factors. However, we found that the architecture of metabolite distribution could be explained by simple evolutionary processes without trait-based mechanisms by comparing our model and the earlier model. Our model provided a better qualitative and quantitative prediction of nested and modular structures in addition to heterogeneous connectivity. This finding implies an alternative possible origin of these structural properties, and suggests the mechanisms underlying establishment metabolite distributions across plant species are simpler than expected.