Fungal endophyte diversity in carnivorous plants

The diversity and role of microbial symbionts has been a significant stepping stone in our understanding of the functionality and evolution of plants. Carnivorous plants have specific adaptations to attract, trap, and digest animal prey to survive in low nutrient environments. Significant gaps in our knowledge exist about the specific mechanisms involved in these different processes. In particular, the presence and role of microbial symbionts in plant carnivory. Fungal endophytes are a ubiquitous fungal group which exist inside host plant tissues and contribute significantly to host plant health, primarily through the production of secondary metabolites. Fungal endophytes exist within carnivorous plant tissues, but research into the diversity and roles of fungal endophytes in carnivorous plants is sparse.

In the largest study of fungal endophyte diversity in carnivorous plants to dte (Chapter 6) I find a much higher diversity of endophytes in carnivorous plant traps than previously understood. From 260 plant samples, over 2000 ASVs were identified representing at least 900 fungal species. High host specificity of endophyte communities was observed. At the site level, endophyte communities were highly host specific, with large turnover of endophyte species between plant hosts, carnivorous and non-carnivorous plant endophyte communities were consistently significantly different. Additionally, there was a high species turnover observed between the same host species growing at different sites, highlighting the impact of different environments on fungal endophyte communities.

In order to achieve this result, first I identified previous studies on endophyte diversity in carnivorous plants (Chapter 2) I report on 11 studies across different sites and from 12 different study species, despite a reliance of culture dependent approaches (which are consistently shown throughout this thesis to underestimate true endophyte diversity), from the 143 endophyte species reported across the studies, only 8 were reported from more than one carnivorous plant species, demonstrating the ubiquity of endophytes in carnivorous plant tissues and suggesting a high degree of host specificity. I identified the secondary metabolites and enzymes known to be produced by the reported endophytes, a non-exhaustive review found over 300 secondary metabolites and over 100 enzymes produced by fungi reported in carnivorous plants, seven of these metabolites already have known uses in plant carnivory, primarily prey attraction, enzymes reported such as chitinase are also used by plants to digest prey. To explore traditional culture dependent approaches, in Chapter 4 I culture fungal endophytes from the traps of carnivorous plants in the UK. I found seven fungal endophyte species across the carnivorous plant species and sites from four genera (Alternaria, Cladosporium, Colletotrichum, and Didymocyrtis). The low number of endophytes cultured make it difficult to draw conclusions on site or host specificity, as endophytes were not consistently recovered from within the plants. In Chapter 5, I compare culture dependent and high throughput sequencing of fungal endophytes in Venus flytraps (Dionaea muscipula) growing in their native range in South Carolina. Both methods were able to identify endophytes from Venus flytraps, however high throughput sequencing reveals significantly higher diversity than culture dependent methods. With culture dependent methods identifying 13 fungal species (primarily Penicillium), whereas high throughput sequencing identified at least 175 species.

The results presented here improve our understanding of the diversity of endophytes found in carnivorous plants by providing the first extensive study of endophytes from carnivorous plant traps, this highlighted the high degree of host specificity of endophytes between different co-occurring carnivorous plant species, with evidence that carnivorous plants with more similar functional traits (trap type) have more similar endophyte communities. This research provides the first step in identifying likely key fungal symbionts in several carnivorous plant species, identifying areas for future research to understand the diversity and roles of this ubiquitous symbiosis in shaping the evolution of plant carnivory.