Physcomitrella patens

Physcomitrella patens
Scientific classification
Kingdom:	Plantae
Division:	Bryophyta
Class:	Bryopsida
Subclass:	Funariidae
Order:	Funariales
Family:	Funariaceae
Genus:	Physcomitrella
Binomial name
Physcomitrella patens (Hedw.) Bruch & Schimp.

Physcomitrella patens is a moss (Bryophyta) used as a model organism for studies on plant evolution, development and physiology. The generic name implies a resemblance to Physcomitrium, which is named, however, for its large calyptra, unlike that of Physcomitrella. [Latin -ella, diminutive, resembling a small Physcomitrium] ^[1]

Model organism

Protonema cells of Physcomitrella patens

Mosses share fundamental genetic and physiological processes with vascular plants, although the two lineages diverged early in land plant evolution.^[2] A comparative study between modern representatives of the two lines can give an insight into the evolution of the mechanisms behind the complexity of modern plants.^[2] It is in this context that Physcomitrella patens is used as a model organism.

Physcomitrella patens is one of a few known multicellular organisms with highly efficient homologous recombination.^[3][4] meaning that an exogenous DNA sequence can be targeted to a specific genomic position (a technique called gene targeting) to create knockout mosses. This approach is called reverse genetics and it is a powerful and sensitive tool to study the function of genes and, when combined with studies in higher plants like Arabidopsis thaliana, can be used to study molecular plant evolution.

The targeted deletion or alteration of moss genes relies on the integration of a short DNA strand at a defined position in the genome of the host cell. Both ends of this DNA strand are engineered to be identical to this specific gene locus. The DNA construct is then incubated with moss protoplasts in the presence of polyethylene glycol (PEG). As mosses are haploid organisms, the regenerating moss filaments (protonemata) can be directly assayed for gene targeting within 6 weeks using PCR methods.^[5] The first study using knockout moss appeared in 1998 and functionally identified ftsZ as a pivotal gene for the division of an organelle in a eukaryote.^[6]

In addition, P. patens is increasingly used in biotechnology. Examples are the identification of moss genes with implications for crop improvement or human health ^[7] and the safe production of complex biopharmaceuticals in moss bioreactors.^[8] By multiple gene knockout Physcomitrella plants were engineered that lack plant-specific post-translational protein glycosylation. These knockout mosses are used to produce complex biopharmaceuticals in a process called molecular farming.^[9]

The genome of Physcomitrella patens, with about 500 megabase pairs organized into 27 chromosomes, was completely sequenced in 2006.^[2][10][11]

Physcomitrella ecotypes, mutants, and transgenics are stored and made freely available to the scientific community by the International Moss Stock Center (IMSC). The accession numbers given by the IMSC can be used for publications to ensure safe deposit of newly described moss materials.

Life cycle

Like all mosses, the life cycle of Physcomitrella patens is characterized by an alternation of two generations: 1) a haploid gametophyte that produces gametes and 2) a diploid sporophyte where haploid spores are produced.

A spore develops into a filamentous structure called protonema, composed of two types of cells – chloronema with large and numerous chloroplasts and caulonema with very fast growth. Protonema filaments grow exclusively by tip growth of their apical cells and can originate side branches from subapical cells. Some side branch initial cells can differentiate into buds rather than side branches. These buds give rise to gametophores (0.5 – 5 mm^[12]), more complex structures bearing leaf-like structures, rhizoids and the sexual organs: female archegonia and male antheridia. Physcomitrella patens is monoicous, meaning that male and female organs are produced in the same plant. If water is available flagellate sperm cells can swim from the antheridia to an archegonium and fertilize the egg within. The resulting diploid zygote originates a sporophyte composed of a foot, seta and capsule, where thousands of haploid spores are produced by meiosis.

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  Cleistocarpous sporophyte of the moss Physcomitrella patens

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  Physcomitrella patens plants growing axenically in vitro on agar plates (Petri dish, 9cm diameter).

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  Moss bioreactor with Physcomitrella patens

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  Four different ecotypes of Physcomitrella patens stored at the International Moss Stock Center

The Polycomb gene FIE is expressed (blue) in unfertilised egg cells of the moss Physcomitrella patens (right) and expression ceases after fertilisation in the developing diploid sporophyte (left). In situ GUS staining of two female sex organs (archegonia) of a transgenic plant expressing a translational fusion of FIE-uidA under control of the native FIE promoter. [13]

Wild-type Physcomitrella and knockout-mosses: Deviating phenotypes induced in gene-disruption library transformants. Physcomitrella wild-type and transformed plants were grown on minimal Knop medium to induce differentiation and development of gametophores. For each plant, an overview (upper row, scale bar corresponds to 1 mm) and a close-up (bottom row, scale bar equals 0.5 mm) is shown. A, Haploid wild-type moss plant completely covered with leafy gametophores and close-up of wild-type leaf. B-D, Different Mutants. [14]

Distribution

Physcomitrella patens is widely distributed in the northern hemisphere.

References

1. ^ http://www.mobot.org/plantscience/bfna/V1/FunaPhyscomitrella.htm
2. ^ ^{a b c} Rensing, S. A., Lang, D., Zimmer, A. D., Terry, A., Salamov, A., Shapiro, H. et al. (2008). The Physcomitrella genome reveals evolutionary insights into the conquest of land by plants. Science, 319(5859), 64-69.
3. ^ Schaefer, D. and Zrÿd J.-P. (1997) Efficient gene targeting in the moss Physcomitrella patens. Plant Journal 11: 1195-1206.
4. ^ Schaefer, D. (2002) A new moss genetics: Mutagenesis in Physcomitrella patens. Annu. Rev. Plant Biol. 53: 477–501,
5. ^ Reinhard, Christina; Schween, Gabriele; Reski, Ralf; Hohe, Annette; Egener, Tanja; Lucht, Jan M.; Holtorf, Hauke (2004). "An improved and highly standardised transformation procedure allows efficient production of single and multiple targeted gene-knockouts in a moss, Physcomitrella patens". Current Genetics 44 (6): 339–47. doi:10.1007/s00294-003-0458-4. PMID 14586556. 
6. ^ Strepp, René; Scholz, Sirkka; Kruse, Sven; Speth, Volker; Reski, Ralf (1998). "Plant Nuclear Gene Knockout Reveals a Role in Plastid Division for the Homolog of the Bacterial Cell Division Protein FtsZ, an Ancestral Tubulin". Proceedings of the National Academy of Sciences of the United States of America 95 (8): 4368–4373. doi:10.1073/pnas.95.8.4368. JSTOR 44902. PMC 22495. PMID 9539743. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=22495. 
7. ^ Ralf Reski and Wolfgang Frank (2005): Moss (Physcomitrella patens) functional genomics – Gene discovery and tool development with implications for crop plants and human health. Briefings in Functional Genomics and Proteomics 4, 48-57. [1]
8. ^ Eva L. Decker and Ralf Reski (2007): Moss bioreactors producing improved biopharmaceuticals. Current Opinion in Biotechnology 18, 393-398. [2]
9. ^ Koprivova, Anna; Stemmer, Christian; Altmann, Friedrich; Hoffmann, Axel; Kopriva, Stanislav; Gorr, Gilbert; Reski, Ralf; Decker, Eva L. (2004). "Targeted knockouts of Physcomitrella lacking plant-specific immunogenic N-glycans". Plant Biotechnology Journal 2 (6): 517–23. doi:10.1111/j.1467-7652.2004.00100.x. PMID 17147624. 
10. ^ JGI
11. ^ Ralf Reski, Merle Faust, Xiao-Hui Wang, Michael Wehe, Wolfgang O. Abel (1994). "Genome analysis of the moss Physcomitrella patens (Hedw.) B.S.G.". Molecular and General Genetics 244 (4): 352–359. doi:10.1007/BF00286686. PMID 8078460. http://www.springerlink.com/content/h1857x41k341xt67/. 
12. ^ Goffinet, Bernard (2005). Physcomitrella Bryophyte Flora of North America, Provisional Publication
13. ^ Assaf Mosquna, Aviva Katz, Eva Decker, Stefan Rensing, Ralf Reski, Nir Ohad (2009): Regulation of stem cell maintenance by the Polycomb protein FIE has been conserved during land plant evolution. Development 136, 2433-2444>
14. ^ Egener, T; Granado, J; Guitton, MC; Hohe, A; Holtorf, H; Lucht, JM; Rensing, SA; Schlink, K et al (2002). "High frequency of phenotypic deviations in Physcomitrella patens plants transformed with a gene-disruption library". BMC plant biology 2: 6. PMC 17800. PMID 12123528. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=17800. 

External links

Wikimedia Commons has media related to: Physcomitrella patens

• The moss genome consortium homepage
• cosmoss.org - moss transcriptome and genome resource including genome browser
• The Japanese Physcomitrella transcriptome resource (Physcobase)
• The NCBI Physcomitrella patens genome project page
• JGI genome browser
• The moss Physcomitrella patens gives insights into RNA interference in plants
• A small moss turns professional
• Physcomitrella patens facts, developmental stages, organs at GeoChemBio
• Tropicos.org. Missouri Botanical Garden.