Metabolites and microbes of Tetrastigma: the ecology of host choice in Rafflesia and potential applications in ex situ conservation of the worlds largest flower

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Amidst the dwindling rainforests of Southeast Asia, Rafflesia’s rare but massive malodorous maroon flower stands out, deceptively luring carrion flies, hence the common name, “corpse flower”. Unlike most plants, Rafflesia is an obligate plant parasite, bereft of stems, roots, and leaves, and devoid of photosynthesis, which supposedly defines plants. Solely infecting the tropical grape vine Tetrastigma—and only a few species of it—it is unknown why. Despite being a charismatic icon of conservation, there is no western botanic garden that has grown Rafflesia because it is still virtually unknown how. This project aims to understand the ecology of Rafflesia’s host choice—what molecules and microbes in Tetrastigma hosts make them susceptible to Rafflesia infection compared to non-hosts, and how this basic information may be used to guide propagation. Conversely, this project will yield data on the metabolic and microbial processes underlying enhanced host immune function in Tetrastigma, why certain species are not parasitized by Rafflesia, and how this knowledge can be applied in grapes, Tetrastigma’s close relative, to resist parasitic infections. Moreover, the project will engage underrepresented students and catalyze their careers in biodiversity science, while providing capacity building to indigenous communities in the Philippines where samples will be collected. This understanding of the fundamental science may one day allow Rafflesia—the panda of the plant world—to be in full bloom in botanic gardens, fostering education and conservation. Timing is critical, because once extinct, the corpse flower can no longer be revived.Rafflesia (Rafflesiaceae, Malpighiales) is an endophytic holoparasite, completely dependent on its host vine Tetrastigma (Vitaceae, Vitales) for nutrition, living inside it throughout its life and only emerging to flower. However, not all Tetrastigma species support a Rafflesia infection. The project aims to understand the ecology of Rafflesia’s host choice, focusing on the chemistry and microbiota unique to infected host species through metabolite profiling and metagenomic analysis. Comparing multiple Rafflesia-Tetrastigma species systems will clarify common patterns that make certain Tetrastigma spp. hosts versus non-hosts, reveal how different Rafflesia spp. similarly alter host ecology during an infection, as well as decipher the metabolic and microbial idiosyncrasies between species systems that could explain Rafflesia’s host choice. In agriculture, grafting success is dependent on how closely related the scion and rootstock are, but how does Rafflesia, belonging to a different order from its host, successfully evade host immunity, and how can this basic information be applied in preventing graft incompatibility in crops? Resulting data will also reveal the extent of convergent evolution compared to other host-parasite systems, if there are similar host-degrading metabolites in the evolution of heterotrophy in disparate lineages of parasitic plants. These data will elucidate host chemotypes and plant-regulating microbial endophytes that could facilitate and sustain a Rafflesia infection, and consequently, Rafflesia horticulture for ex situ conservation while gaining insights that could potentially benefit other agricultural crops.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.