Compartmentalization of specialized metabolites across vegetative and reproductive tissues in two sympatricPsychotria(Rubiaceae)

Premise of the study The specialized metabolites of plants are recognized as key chemical traits in mediating the ecology and evolution of sundry plant-biotic interactions, from pollination to seed predation. Intra- and interspecific patterns of specialized metabolite diversity have been studied extensively in leaves, but the diverse biotic interactions which contribute to specialized metabolite diversity encompass all plant organs. Focusing on two species of Psychotria shrubs, we investigate and compare patterns of specialized metabolite diversity in leaves and fruit with respect to each organ’s diversity of biotic interactions. Methods To evaluate associations between biotic interaction diversity and specialized metabolite diversity, we combine UPLC-MS metabolomic analysis of foliar and fruit specialized metabolites with existing surveys of leaf- and fruit-centered biotic interactions. We compare patterns of specialized metabolite richness and variance among vegetative and reproductive tissues, among plants, and between species. Key results In our study system, leaves are involved in a greater number of host-specific biotic interactions than fruit, while fruit-centric interactions are more ecologically diverse. This was reflected in specialized metabolite richness – leaves contained more than fruit, while each contained over 200 organ-specific specialized metabolites. Within each species, leaf- and fruit specialized metabolite composition varied independently of one another across plants. Specialized metabolite composition exhibited stronger contrasts between organs than between species. Conclusions As ecologically disparate plant organs with organ-specific specialized metabolite traits, leaves and fruit can each contribute to the tremendous overall diversity of plant specialized metabolites.