CORE Metadata, citation and similar papers at core.ac.uk Provided by Copenhagen University Research Information System Mitochondrial genome evolution in parasitic plants Zervas, Athanasios; Petersen, Gitte; Seberg, Ole Published in: BMC Evolutionary Biology DOI: 10.1186/s12862-019-1401-8 Publication date: 2019 Document version Publisher's PDF, also known as Version of record Document license: CC BY Citation for published version (APA): Zervas, A., Petersen, G., & Seberg, O. (2019). Mitochondrial genome evolution in parasitic plants. BMC Evolutionary Biology, 19, [87]. https://doi.org/10.1186/s12862-019-1401-8 Download date: 09. Apr. 2020 Zervas et al. BMC Evolutionary Biology (2019) 19:87 https://doi.org/10.1186/s12862-019-1401-8 RESEARCH ARTICLE Open Access Mitochondrial genome evolution in parasitic plants Athanasios Zervas* , Gitte Petersen and Ole Seberg Abstract Background: Parasitic plants rely on their host to cover their nutritional requirements either for their entire life or a smaller part of it. Depending on the level of parasitism, a proportional reduction on the plastid genome has been found. However, knowledge on gene loss and evolution of the mitogenome of parasitic plants is only available for four hemiparasitic Viscum species (Viscaceae), which lack many of the mitochondrial genes, while the remaining genes exhibit very fast molecular evolution rates. In this study, we include another genus, Phoradendron, from the Viscaceae, as well as 10 other hemiparasitic or holoparasitic taxa from across the phylogeny of the angiosperms to investigate how fast molecular evolution works on their mitogenomes, and the extent of gene loss. Results: Our observations from Viscum were replicated in Phoradendron liga, whereas the remaining parasitic plants in the study have a complete set of the core mitochondrial genes and exhibit moderate or only slightly raised substitution rates compared to most autotrophic taxa, without any statistically significant difference between the different groups (autotrophs, hemiparasites and holoparasites). Additionally, further evidence is provided for the placement of Balanophoraceae within the order Santalales, while the exact placement of Cynomoriaceae still remains elusive. Conclusions: Weexaminethemitochondrialgenecontentof11hemiparasitic and holoparasitic plants and confirm previous observations in Viscaceae. We show that the remaining parasitic plants do not have significantly higher substitution rates than autotrophic plants in their mitochondrial genes. We provide further evidence for the placement of Balanophoraceae in the Santalales. Keywords: Phylogeny, Parasitic plants, Substitution rates, Evolution, Parasitism, Balanophoraceae, Viscaceae, Mitogenome Background holoparasite Rafflesia lagascae Blanco [6], comparatively lit- Parasitic plants comprise around 1% of all angiosperm spe- tle attention has been given to mitochondrial evolution. cies (http://parasiticplants.siu.edu/ParPlantNumbers.pdf). The plastome of a typical, autotrophic angiosperm is cir- Depending on their photosynthetic ability, they are catego- cular, of a rather uniform size, and has a relatively con- rized as hemiparasites (facultative or obligatory) and holo- served structure, with two unique regions separated by parasites. Current phylogenetic evidence suggests that two inverted repeats, as well as a conserved gene content parasitism has evolved independently at least 12 times [1, of ca. 40 protein coding genes, four rRNA genes and ap- 2], offering an excellent framework for studies of correl- proximately 20 tRNA genes [7–9]. However, plastomes of ation between parasitism and genomic evolution. While a the numerous parasitic angiosperms that have been se- series of papers have recently focused on the correlation be- quenced show a pronounced variation both in size, struc- tween levels of parasitism and loss of key photosynthesis ture and gene content. Not unexpectedly, there is a clear genes in the plastome [3–5] and an instance of a possible correlation between the type of parasitism and the level of complete loss of the plastome has also been reported in the plastome reduction and modification, e.g. plastomes of the holoparasitic members of Orobanchaceae [10], Cus- cuta L. [3, 4], Pilostyles Guil. [11], Rafflesia lagascae [6], * Correspondence: [email protected] Hydnora visseri Bolin, E.Maass & Musselman [12], and The Natural History Museum of Denmark, Faculty of Science, University of Copenhagen, Sølvgade 83, opg. S, DK-1307 Copenhagen K, Denmark others, are much more reduced and modified than © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Zervas et al. BMC Evolutionary Biology (2019) 19:87 Page 2 of 14 plastomes of hemiparasitic members of Orobanchaceae autotrophic land plants [23], while the remaining genes [5] and Viscaceae [13]. Similar evolutionary plastome re- comprise a variable part of the plant mitogenome. This ductions have been described in achlorophyllous mycohe- was also observed in the holoparasitic plants Rafflesia terotrophic plants, which have either functionally or lagascae [6] and Cynomorium coccineum [24], and simi- completely lost most or all genes involved in photosyn- lar results have been reported for three hemiparasitic thesis, e.g., Neottia nidus-avis (L.) Rich. [14], Corallorhiza and three holoparasitic Orobanchaceae, all of which pos- striata Lindl. [15], Petrosavia stellaris Becc. [16], and sev- sessed a complete core mitochondrial gene set [25]. eral members of Ericaceae [17]. In hemiparasitic plants, However, recent studies on four species of Viscum capable of photosynthesis, major plastome reductions showed a surprising reduction in gene content compared would not be expected, but nevertheless a recent study of to all other known angiosperm mitogenomes [26, 27]. the Santalales, and specifically on the hemiparasitic genera This observation prompts the obvious question, whether Osyris L. and Viscum showed that their plastomes are re- a loss of genes in the mitogenome similar to that ob- duced by 10–22% compared to Vitis [13]theclosestauto- served in the Viscaceae is found in other parasitic line- trophicrelativesequenced. ages as well. Evolution of the mitochondrial genomes, henceforth In addition to extensive gene loss, a very high level of se- mitogenomes, which are involved in basic cell metabol- quence divergence of the remaining key genes was also ism, was not expected to be influenced by parasitism. observed in the four species of Viscum [26, 27]. Especially Mitochondria are essential producers of the energy the genes in respiratory complex V, atp1, apt6, atp8, and (ATP) of the cell and harbour key metabolic genes that atp9, have very high substitution rates compared to other control respiration, stress responses, and additionally plants. However, a few genes, e.g. matR in V. album L., re- defence against microorganisms and aspects of pro- tain a low substitution rate. In general, mitochondrial ge- grammed cell apoptosis. Compared to plant mitochon- nomes have low substitution rates, lower than what is drial genomes, animal mitochondrial genomes are in found in the chloroplast genomes, and 10–20 times lower general fairly small in size (ca. 16 kb long), uniform in compared to the plant nuclear genomes [28]. Often, structure (circular) and gene content, encoding 22 tRNA higher substitution rates in the mitogenome are accom- genes, two rRNA genes and usually 13 protein coding panied by higher substitution rates in the other two plant genes of the respiratory chain complexes I: nad1, nad2, genomes, and are inferred to be a characteristic of the spe- nad3, nad4, nad4L, nad5, nad6, III: cob,IV:cox1, cox2, cies that exhibits them, e.g. in certain species of Plantago cox3, and V: atp6,andatp8 [18]. In contrast, plant mito- L. [29]. However, it has been shown later that certain plant genomes exhibit profound differences: Their size is 10 to genera, like Pelargonium L. H. Bailey, have high substitu- almost 1000 times larger than their animal counterparts, tion rates only in their mitogenomes [30]. Comparison of ranging from less than 200 kb to some 11.3 mb as in the nuclear small-subunit rDNA from partially autotrophic, case of Silene conica L. [19]. This has been partly attrib- chlorophyllous hemiparasites, and achlorophyllous holo- uted to the presence of larger introns, of more repeated parasites showed that the latter have much higher substi- sequences, and stretches of DNA transferred either from tution rates than the former [31]. Higher chloroplast the nuclear and chloroplast genome, or from bacteria substitution rates have been suggested to be correlated and viruses that have infected the plant [19, 20]. Elec- with species richness, as in the case of the Proteaceae [32]. tron microscopy and DNA sequencing has revealed that Early theoretical models have suggested that parasites plant mitogenomes may be circular, linear, branching should evolve much faster than their hosts as a response and comprising one or more molecules,