Scientists from Norway (UiT, The Arctic University of Norway), Germany (RWTH Aachen, Research Center Jülich, Helmholz Center, Technical University in Munich) and Austria (University of Vienna) have sequenced the genome of the parasitic flowering plant Cuscuta campestris. The work was led by parasitic plant researcher Prof. Kirsten Krause (UiT), and by genome expert Prof. Björn Usadel (RWTH) and was recently published in the high ranking journal Nature Communications (DOI: 10.1038/s41467-018-04344-z).
Along with numerous other plants species, C. campestris survives by infecting other plants and by stealing the nutrients that these produce by using the energy of the sunlight. Parasitic plants threaten crops production in many countries across the globe due to the damage they inflict on their victims. Like many other parasites, C. campestris is optimally adapted to its ecological niche. Most noticeably, it possesses specialized feeding organs that are absent in other plants. On the other hand it lacks some organs that other plants usually have, such as true leaves and roots.
The C. campestris genome sequence is the first one of a parasitic plant that has been released. It provides insight into the unique genomic footprint that the parasitic lifestyle has left in these unusual plants. One remarkable result is the finding that during its evolution, the parasite has taken up genome fragments from its hosts and incorporated them into its own genome – sometimes in smaller portions and sometimes in bigger chunks. This process, known as horizontal gene transfer (HGT), has equipped Cuscuta with new genetic material which may have given Cuscuta an advantage in their struggle to remain undiscovered by the host. From their careful analysis in the future we will be able to learn whether the parasite has selected genes that were beneficial for its survival, be it to conceal it from the host or be it to widen its repertoire of biomass-degrading enzymes.
Another finding is that more than 1700 genes that are otherwise highly conserved among land plants, are missing in the genome of the parasite. Many losses occur in functional clusters give evidence for the consequences of the independence of the parasites from, for example, photosynthesis.
With the insight that this genome gives researchers, they will be able to understand how this parasite can be so harmful to its host plants. Along with this understanding, it will be possible to develop new approaches to help farmers overcome this devastating weed.
During a sabbatical the group leader of the TFS-Enigma project Prof. Kirsten Krause is visiting the working group of Dr. Markus Albert at the University of Tübingen, Germany. She will learn new methods there, which will increase the spatial resolution of our expression analyses.
Working group of Dr. Markus Albert
Answers to these fundamental questions can come from an unusual group of flowering plants: parasites of the genus Cuscuta (dodder).
Cuscuta spec. (yellow) spiralling around a host plant stem (green).
Several unique features enable parasitic plants to infect other plants and live heterotrophically from what these hosts provide. The most amazing phenomenon was the development of feeding organs that connect parasite and host physically and physiologically.
A Cuscuta reflexa suction cup (top) attaching firmly to a host stem (bottom). The cone-shaped feeding organ which protrudes from the middle of the suction cup and grows into the the host is invisible in this view. B The cone-shaped feeding organ visualized by light microscopy after cross-sectioning an infection site. The parasitic tissue is highlighted in yellow. C Despite their close entanglement (right) can parasite and host tissue be distinguished using fluorescence labelled antibodies (left).
The technical term, “haustorium”, that is derived from the latin “haurire” which means “to drink”, reflects its main function well. This cone-shaped organ essentially fulfills a similar function as roots do in other plants. For this they establish intimate cellular connections to the host tissue. The ability of Cuscuta to manipulate cells of plants from unrelated taxa across wide parts of the plant kingdom into forming open cellular connections with the haustorial surface cells is one of the fundamental aspects of plant biology that is still poorly understood. The “TFS-Enigma” project will focus on this enigmatic phenomenon and will close this important gap. During the project, we will develop knowledge and methodology related to the analysis of the host-parasite interface.