Chloroplast DNA

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Is fachsprachlich as chloroplast DNA or plastid DNA short ctDNA or cpDNA , the double-stranded, generally circular DNA inside ( stroma ) of the chloroplast (or more generally plastids hereinafter). The chloroplast / plastid genome is called a plastome . With a few exceptions, chloroplasts and other plastids contain their own DNA.

Plastid DNA was first detected in 1962. A plastome was sequenced for the first time in 1986 when two Japanese research teams sequenced the chloroplast DNA of Marchantia polymorpha (fountain liver moss , liverwort ) and Nicotiana tabacum (tobacco, nightshade family ). Since then, hundreds of chloroplast DNAs from different species have been sequenced. Most of the time, however, these are chloroplastida , i. H. Land plants or green algae . Glaucophytes (Glaucophyta), red algae (Rhodophyta syn. Rhodophyceae) and other groups of algae are strongly underrepresented.

Molecular structure

Gene map of chloroplast DNA from tobacco according to Wakasugi et al. Segments with labels on the outside are on the A-leg, segments with labels on the inside are on the B-leg. Segments that are narrower than those around them (the notches) indicate introns. Unlabeled pale segments represent open reading frames .

In the chloroplastida (including the green algae and land plants ), the chloroplasts usually have their entire genome combined into a single large DNA ring, which is usually 120,000–170,000  bp (base pairs) long. The contour length is around 30 to 60 µm, the mass around 80 to 130  MDa (million Dalton).

Although chloroplast DNA is normally assumed to be a circular molecule, there is evidence that it could often have a linear shape, especially in other groups such as the glaucophytes or red algae mentioned.

Reverse copies (inverted repeats)

In most photosynthetic organisms, the chloroplast genome has a four-part structure. These are two opposing copies ( English inverted repeats ), which separate a long single copy section ( English long single copy section , LSC) from a short single copy section ( English short single copy section , SSC).

The sizes of the three different DNA regions can vary from species to species up to the complete loss of the copied regions. The inverted repeats range in length from 4 to 25  kbp , with only four to over 150 genes each. Inverted repeats in plants tend to be at the higher end of this scale and are each 20 to 25 kbp long. However, among land plants, the inverted repeats are highly conserved and only accumulate a few mutations. Similar inverted repeats as in green algae and land plants are found in the genome of cyanobacteria and the two other chloroplast lines ( glaucophytes and red algae , see below), which suggests that the inverted repeats are older than the chloroplasts, even if some chloroplast lines have these features of their DNA since then lost or flipped them (back to direct reps). Perhaps the inverted repeats are helping to stabilize the rest of the chloroplast genome: chloroplast DNAs some of the inverted repeats have lost, tend to rearrange themselves ( English DNA rearrangement ).

Nucleoids

New chloroplasts can contain up to 100 copies of their DNA, although their number decreases to around 15 to 20 as the chloroplasts age. As with prokaryotes, they are usually packed in nucleoids (nuclear equivalents, here: chloroplast nucleoids or cp nucleoids for short), which can contain several identical chloroplast DNA rings. There are also a number of such nucleoids in every chloroplast. In primitive red algae, the cp nucleoids are located in the center of the chloroplast, while in green plants and green algae the cp nucleoids are distributed throughout the stroma.

The DNA of chloroplasts, as well as bacteria and mitochondria , is not associated with real histones (these are only found in the cell nuclei of eukaryotes and in precursors in archaea ). The tight packing of the DNA into a nucleoid in these groups is brought about by proteins, whose function is therefore histone-like (i.e., analogous to histones). These are HU in bacteria ABF2 in mitochondria and HC ( acronym for English h iStone-like protein of c hloroplast ) in the chloroplasts of red algae as Cyanidioschyzon merolae ( Cyanidiales ). The histone-like proteins (HLPs, from English h istone l ike p roteins ) of these three groups are in turn homologous to one another , i. H. a common evolutionary origin of the HLPs is assumed.

DNA repair

In chloroplasts of the moss Physcomitrella patens ( Physcomitrella patens ) that interacts DNA mismatch repair protein (MMR protein) MSH1 with the recombinant repair proteins RecA and recG to obtain the stability of the chloroplast genome. In chloroplasts of the plant thale cress ( Arabidopsis thaliana ) RecA protein maintains the integrity of the chloroplast DNA by a process upright, which probably contains the recombinant repair of DNA damage.

DNA-free plastids

In 2014 a plastid without a genome was even found in the non-photosynthetically active green alga Polytomella ( Chlamydomonadales , syn. Volvocales). Apparently, chloroplasts / plastids can lose their entire genome through endosymbiotic gene transfer.

See also

Individual evidence

  1. ^ The Oxford Dictionary of Abbreviations 1998.
  2. ↑ C. Cleveland (ed.); C. Michael Hogan, S. Draggan: DNA , The Encyclopedia of Earth, National Council for Science and the Environment . Washington DC, July 18, 2012 (via WebArchive)
  3. ↑ a b c Leighton Then: Green DNA - Simple isolation, restriction and electrophoresis of chloroplast DNA . BIOSCIENCE EXPLAINED, Science and Plants for Schools, Homerton College, Cambridge 2002. (via WebArchive)
  4. ↑ Chloroplasts and Other Plastids . (via WebArchive)
  5. ↑ a b c d e f g Anna Stina Sandelius, Henrik Aronsson: The Chloroplast: Interactions with the Environment . Springer, 2009, ISBN 978-3-540-68696-5 , p. 18.
  6. ↑ T. Wakasugi, M. Sugita, T. Tsudzuki, M. Sugiura: Updated Gene Map of Tobacco Chloroplast DNA , in: Plant Molecular Biology Reporter, Volume 16, Issue 3, pp. 231-241, September 1998. doi: 10.1023 / A: 1007564209282
  7. ↑ MT Clegg, BS Gaut, GH Learn Jr, BR Morton: Rates and Patterns of Chloroplast DNA Evolution . In: Proceedings of the National Academy of Sciences . 91, No. 15, 1994, pp. 6795-6801. bibcode : 1994PNAS ... 91.6795C . doi : 10.1073 / pnas.91.15.6795 . PMID 8041699 . PMC 44285 (free full text).
  8. ↑ a b c d J. Shaw, EB Lickey, EE Schilling, RL Small: Comparison of whole chloroplast genome sequences to choose noncoding regions for phylogenetic studies in angiosperms: The tortoise and the hare III . In: American Journal of Botany . 94, No. 3, 2007, pp. 275-288. doi : 10.3732 / ajb.94.3.275 . PMID 21636401 .
  9. ^ Ron Milo, Rob Philips: Cell Biology by the Numbers: How large are chloroplasts? . Retrieved March 16, 2019.
  10. ↑ a b Jeremy Burgess: An introduction to plant cell development . Cambridge university press, Cambridge 1989, ISBN 0-521-31611-1 , p. 62.
  11. ↑ Arnold J. Bendich: Circular chloroplast Chromosomes: The Grand Illusion . In: The Plant Cell Online . 16, No. 7, 2004, pp. 1661-6. doi : 10.1105 / tpc.160771 . PMID 15235123 . PMC 514151 (free full text).
  12. ↑ a b c Richard Kolodner, Krishna K. Tewari: Inverted Repeats in Chloroplast DNA from Higher Plants . In: Proceedings of the National Academy of Sciences . 76, No. 1, 1979, pp. 41-5. bibcode : 1979PNAS ... 76 ... 41K . doi : 10.1073 / pnas.76.1.41 . PMID 16592612 . PMC 382872 (free full text).
  13. ↑ a b Jeffrey D. Palmer, William F. Thompson: Chloroplast DNA rearrangements are more frequent when a large inverted repeat sequence is lost . In: Cell . 29, No. 2, 1982, pp. 537-50. doi : 10.1016 / 0092-8674 (82) 90170-2 . PMID 6288261 .
  14. ^ Hans-Walter Heldt, Fiona Heldt, Birgit Piechulla: Plant Biochemistry , 3rd edition, Academic Press, 2005, ISBN 978-0-12-088391-2 , p. 517.
  15. ↑ a b T. Kobayashi, M. Takahara, SY Miyagishima, H. Kuroiwa, N. Sasaki, N. Ohta, M. Matsuzaki, T. Kuroiwa: Detection and Localization of a Chloroplast-Encoded HU-Like Protein That Organizes Chloroplast Nucleoids . In: The Plant Cell Online . 14, No. 7, 2002, pp. 1579-1589. doi : 10.1105 / tpc.002717 . PMID 12119376 . PMC 150708 (free full text).
  16. ^ Biology, 8th Edition, Campbell & Reece . Benjamin Cummings (Pearson), 2009, ISBN 978-0-321-54325-7 , p. 516.
  17. ↑ John M. Archibald: The Puzzle of Plastid Evolution . In: Current Biology . 19, No. 2, 2009, pp. R81-8. doi : 10.1016 / j.cub.2008.11.067 . PMID 19174147 .
  18. ↑ Masaki Odahara, Yoshihito Kishita, Yasuhiko Sekine: MSH1 maintains organelle genome stability and genetically interacts with RECA and RECG in the moss Physcomitrella patens . In: Plant J . 91, No. 3, August 2017, pp. 455-465. doi : 10.1111 / tpj.13573 . PMID 28407383 .
  19. ↑ Beth A. Rowan, Delene J. Oldenburg, Arnold J. Bendich: RecA maintains the integrity of chloroplast DNA molecules in Arabidopsis . In: J. Exp Bot.. . 61, No. 10, June 2010, pp. 2575-88. doi : 10.1093 / jxb / erq088 . PMID 20406785 . PMC 2882256 (free full text).
  20. ↑ David Roy Smith, Robert W. Lee: A Plastid without a Genome: Evidence from the Nonphotosynthetic Green Algal Genus Polytomella . In: Plant Physiology . 164, No. 4, April 1, 2014, pp. 1812-1819. doi : 10.1104 / pp.113.233718 . PMID 24563281 . PMC 3982744 (free full text).