Written by Emily Seward at the University of Oxford. This is the report from a BSPP Junior Fellowship. Click here to read more/apply for one yourself.
Phytomonas are single-celled eukaryotic parasites found globally in a broad range of plant hosts. They are transmitted between plants by insect vectors of the order Heteroptera and are known to infect more than 100 plant species from 24 different families. However little is known of their biology, host range or evolutionary history.
Importantly, limited sampling has been conducted outside of South America, where several species cause economically important plant pathologies. Though two species are pathogenic the remainder of Phytomonas appear to cause no deleterious effect on their plant hosts and the mechanism by which they avoid triggering plant immune responses is unknown. Moreover, as this group of parasites do not generally cause pathologies, they have been overlooked by the scientific community and it is unknown whether there are species present in the UK.
The BSPP junior fellowship allowed me to learn the techniques required for sampling and characterisation of Phytomonas from the wild. This was made possible by collaboration with the world experts in isolation, identification and culturing of Phytomonas, Professor Julius Lukeš, Dr. Jan Votýpka and Dr. Petr Kment.
The trip began with the 45th Annual Protistology meeting in Dubovice, about 2 hours south of Prague. There I presented my work on comparative genomics of South American Phytomonas species. This allowed me to gain valuable presentation experience and gather feedback from a range of scientists with expertise on parasitic organisms. I was awarded a prize for my talk and established useful connections with scientists who have complementary research areas and are interested in future collaborations.
Once the conference was concluded I made my way to Prague. There both Jan Votýpka and Petr Kment, the two scientists who coordinated the Phytomonas isolation expedition, met me and outlined the basis of our plan. We were to sample over a dozen sites in the southern region of the Czech Republic, primarily looking for the insect Oxycarenus lavaterae but also other Heteropteran insects, the known vectors of Phytomonas. This strategy of sampling from insects was adopted as Phytomonas can colonise a large diversity of plant tissues (including phloem, latex ducts, fruit, flowers and seeds) and thus sampling the right tissue from plants in the wild can be difficult (Phytomonas eluded discovery until 1909). Moreover, by looking in the insect host, where Phytomonas parasites can reach high infection loads in the gut and salivary glands, it enabled a more rapid and high throughput identification of parasites.
Over the following week we sampled insects from a variety of habitats and locations in the southern regions of the Czech Republic. The most easily collected species was Oxycarenus lavaterae as it overwinters in colonies on the trunk of lime trees (Tilia) (see front cover image) though we also used sweep nets and quick reflexes to collect other insect species.
Once back in the lab we dissected the insects and determined if they had a Phytomonas infection using microscopic analysis of insect tissue. I quickly learnt the tricks associated with accurate dissection of the insect digestive tract and salivary glands and was delighted to find multiple instances of Phytomonas infections in both Oxycarenous lavaterae and Tritomegas sexmaculatus.
Not only were we able to successfully find a wild species of Phytomonas in the Czech Republic, the Phytomonas we discovered in O. lavaterae is a new species with a striking and unusual morphology (see image). Furthermore, a phylogenetic tree using analysis of the small ribosomal subunit sequence indicates that the newly discovered Phytomonas species is basal to other currently described species. This has exciting implications for improving our understanding of Phytomonas biology, particularly with respect to adaptation to different plant hosts.
Overall this was a highly successful trip. It not only led to the discovery of a new species of Phytomonas, but also taught me the skills that are necessary to apply this type of sampling to insects in the UK. By improving our understanding of Phytomonas biology I hope to uncover how this fascinating group of plant parasites thrive in such a diverse range of hosts without provoking plant immune responses. This work was only possible thanks to the BSPP junior fellowship and the help and expertise of the Lukeš and Votýpka labs.
Emily Seward
University of Oxford
TOP IMAGE: Sweep netting and searching for insects in the undergrowth.
An Oxycarenous lavaterae colony on the trunk of a lime tree. Colonies can be made up of several thousand individuals.
Giemsa stained Phytomonas isolated from Oxycarenous lavaterae. It has an unusual morphology that is much more elongated than other Phytomonas species described so far.
