Gitte PetersenUniversitetslektor

Parasitic plants

My current research is primarily focused on parasitic plants and their evolution at the genomic level. Parasitic plants obtain part of or all of their nutrients from another plant or via mycorrhiza forming fungi (mycoheterotrophic parasites). One of the most well-known parasitic plants is the European Mistletoe, Viscum album.

Fruits, germinating seeds and mature plants of European mistletoe, Viscum album (Sv: mistel)

 

While the mistletoe is capable of doing photosynthesis and hence green, other parasitic plants have lost photosynthesis completely and appear pale although the flowers may be brightly coloured.

 

 

 

 

 

 

Yellow bird’s-nest, Monotropa hypopitys (Sv: tallört), a common mycoheterotrophic parasite in Sweden

 

Co-evolution of parasites and hosts provides an excellent system to investigate diversification and genotypic changes associated with heterotrophy, but the development and host interactions of parasitic plants are yet relatively unexplored genetically. While it is increasing well documented that the chloroplast genome, housing a suite of genes involved in photosynthesis, degrades when photosynthesis becomes redundant, less is known about evolutionary consequences of parasitism for the mitochondrial and nuclear genomes. Surprisingly the mitochondrial genome of mistletoe has also lost a number of genes although these would appear essential due to their function in cell respiration.

The current research project includes evolutionary studies of all three genomes in a range of parasitic plants, but with a special emphasis on mistletoes and their closest relatives.

 

Mitochondrial evolution

The mitochondrial genome of flowering plants is far less known than the chloroplast genome. It has an astonishing variation in size and structure, and due to a phenomenon called RNA editing one of the central dogma in molecular biology – the 1:1 correspondence of DNA and RNA – is broken. The mitochondrial genome is also capable of incorporating DNA from other genomes even from other species (horizontal gene transfer).

My current studies of mitochondrial evolution includes parasitic as well as non-parasitic plants.

 

Other projects

Besides parasitic plants, I have a long track record of research in monocot phylogenetics. This has included species level phylogenetics of cereal grasses such as barley (Hordeum), wheat (Triticum) and rye (Secale), but also other monocots e.g., Crocus, Colchicum and selected orchids. At higher taxonomic levels I have done phylogenetic studies of e.g., Alismatales, Asparagales, Liliales and the monocots at large.

DNA barcoding is proposed as a molecular tool for species identification and discovery. I was part of the working group selecting the currently accepted markers and I investigate the limits of the method in selected groups of plants.

 

 

Selected recent publications

 

Petersen, G., Zervas, A., Pedersen, H.Æ. & Seberg, O. 2018. Contracted genes and dwarfed plastome in mycoheterotrophic Sciaphila thaidanica (Triuridaceae, Pandanales). Genome Biology and Evolution 10: 976-981. DOI:10.1093/gbe/evy064

Petersen, G., Cuenca, A., Zervas, A., Ross, T.G., Graham, S.W., Barrett, C.F., Davis, J.I. & Seberg, O. 2017. Mitochondrial genome evolution in Alismatales: size reduction and extensive loss of ribosomal protein genes. – PLoS ONE 12(5): e0177606. DOI:10.1371/journal.pone.0177606

Cuenca, A., Ross, T.G., Graham, S.W., Barrett, C.F., Davis, J.I., Seberg, O. & Petersen, G. 2016. Localized retroprocessing as a model of intron loss in the plant mitochondrial genome. – Genome Biology and Evolution 8: 2176-2189. DOI: 10.1093/gbe/evw148

Petersen, G., Seberg, O., Cuenca, A., Stevenson, D.W., Thadeo, M., Davis, J.I., Graham, S. & Ross, T.G. 2016. Phylogeny of the Alismatales (Monocotyledons) and the relationship of Acorus (Acorales?). – Cladistics 32: 141-159. DOI: 10.1111/cla.12120

Petersen, G., Cuenca, A., Møller, I.M. & Seberg, O. 2015. Massive gene loss in mistletoe (Viscum, Viscaceae) mitochondria. – Scientific Reports 5:17588. DOI: 10.1038/srep17588

Petersen, G., Cuenca, A. & Seberg, O. 2015. Plastome evolution in hemiparasitic Mistletoes. – Genome Biology and Evolution 7: 2520-2532. DOI:10.1093/gbe/evv165

Cuenca, A., Petersen, G. & Seberg, O. 2013. The Complete Sequence of the Mitochondrial Genome of Butomus umbellatus – a Member of an Early Branching Lineage of Monocotyledons. – PLoS ONE 8(4): e61552. DOI:10.1371/journal.pone.0061552.

Petersen, G., Seberg, O. & Davis, J.I. 2013. Phylogeny of the Liliales (Monocotyledons) with a special emphasis on data partition congruence and RNA editing. – Cladistics 29: 274-295. DOI:10.111/j.1096-0031.22012.00427.x