Physcomitrella patens
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''Physcomitrium patens'', (synonym: ''Physcomitrella patens'' ) the spreading earthmoss, is a
moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
(bryophyte) used as a
model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...
for studies on plant evolution, development, and physiology.


Distribution and ecology

''Physcomitrella patens'' is an early colonist of exposed mud and earth around the edges of pools of water. ''P. patens'' has a
disjunct distribution In biology, a taxon with a disjunct distribution is one that has two or more groups that are related but considerably separated from each other geographically. The causes are varied and might demonstrate either the expansion or contraction of a s ...
in
temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
parts of the world, with the exception of South America. The standard laboratory strain is the "Gransden" isolate, collected by H. Whitehouse from Gransden Wood, in
Cambridgeshire Cambridgeshire (abbreviated Cambs.) is a Counties of England, county in the East of England, bordering Lincolnshire to the north, Norfolk to the north-east, Suffolk to the east, Essex and Hertfordshire to the south, and Bedfordshire and North ...
in 1962.


Model organism

Mosses share fundamental genetic and physiological processes with
vascular plants Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They al ...
, although the two lineages diverged early in land-plant evolution. A comparative study between modern representatives of the two lines may give insight into the evolution of mechanisms that contribute to the complexity of modern plants. In this context, ''P. patens'' is used as a
model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...
. ''P. patens'' is one of a few known
multicellular organisms A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- ...
with highly efficient
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
. meaning that an exogenous
DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...
can be targeted to a specific genomic position (a technique called
gene targeting Gene targeting (also, replacement strategy based on homologous recombination) is a genetic technique that uses homologous recombination to modify an endogenous gene. The method can be used to delete a gene, remove exons, add a gene and modify i ...
) to create knockout mosses. This approach is called
reverse genetics Reverse genetics is a method in molecular genetics that is used to help understand the function(s) of a gene by analysing the phenotypic effects caused by genetically engineering specific nucleic acid sequences within the gene. The process pr ...
and it is a powerful and sensitive tool to study the function of
genes In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
and, when combined with studies in higher plants such as ''
Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter a ...
'', can be used to study molecular plant
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
. The targeted deletion or alteration of moss genes relies on the integration of a short DNA strand at a defined position in the
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
of the host cell. Both ends of this DNA strand are engineered to be identical to this specific
gene locus In genetics, a locus (plural loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total ...
. The DNA construct is then incubated with moss protoplasts in the presence of
polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...
. As mosses are
haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
organisms, the regenerating moss filaments ( protonemata) can be directly assayed for gene targeting within 6 weeks using PCR methods. The first study using knockout moss appeared in 1998 and functionally identified ''
ftsZ FtsZ is a protein encoded by the ''ftsZ'' gene that assembles into a ring at the future site of bacterial cell division (also called the Z ring). FtsZ is a prokaryotic homologue of the eukaryotic protein tubulin. The initials FtsZ mean "Filamen ...
'' as a pivotal gene for the division of an
organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
in a
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
. In addition, ''P. patens'' is increasingly used in
biotechnology Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof and molecular analogues for products and services. The term ''biotechnology'' was first used b ...
. Examples are the identification of moss genes with implications for crop improvement or human health and the safe production of complex
biopharmaceutical A biopharmaceutical, also known as a biological medical product, or biologic, is any pharmaceutical drug product manufactured in, extracted from, or semisynthesized from biological sources. Different from totally synthesized pharmaceuticals, t ...
s in
moss bioreactor A moss bioreactor with '' Physcomitrella patens'' A moss bioreactor is a photobioreactor used for the cultivation and propagation of mosses. It is usually used in molecular farming for the production of recombinant protein using transgenic moss. ...
s. By multiple gene
knockout A knockout (abbreviated to KO or K.O.) is a fight-ending, winning criterion in several full-contact combat sports, such as boxing, kickboxing, muay thai, mixed martial arts, karate, some forms of taekwondo and other sports involving striking, a ...
''Physcomitrella'' plants were engineered that lack plant-specific post-translational protein
glycosylation Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not al ...
. These knockout mosses are used to produce complex biopharmaceuticals in a process called molecular farming. The genome of ''P. patens'', with about 500 megabase pairs organized into 27 chromosomes, was completely sequenced in 2008. ''Physcomitrella''
ecotype In evolutionary ecology, an ecotype,Greek: ''οίκος'' = home and ''τύπος'' = type, coined by Göte Turesson in 1922 sometimes called ecospecies, describes a genetically distinct geographic variety, population, or race within a specie ...
s, mutants, and
transgenics A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques. The exact definition of a genetically modified organism and what constitutes genetic engineering varies, with ...
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.


Lifecycle

Like all mosses, the lifecycle of ''P. patens'' is characterized by an alternation of two generations: a
haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...
that produces
gametes A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
and a
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...
where haploid
spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
are produced. A spore develops into a filamentous structure called
protonema A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses. When a moss first grows from a spore, it starts as a ''germ tube'', ...
, 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 Tip commonly refers to: * Tip (gambling) * Tip (gratuity) * Tip (law enforcement) * another term for Advice Tip or TIP may also refer to: Science and technology * Tank phone, a device allowing infantry to communicate with the occupants of an armo ...
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 (0.5–5.0 mm), more complex structures bearing leaf-like structures, rhizoids, and the sexual organs: female
archegonia An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...
and male
antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...
. ''P. patens'' is
monoicous Monoicy () is a sexual system in haploid plants (mainly bryophytes) where both sperm and eggs are produced on the same gametophyte, in contrast with dioicy, where each gametophyte produces only sperm or eggs but never both.Crandall-Stotler, B.J ...
, 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 Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
.


DNA repair and homologous recombination

''P. patens'' is an excellent model in which to analyze repair of DNA damages in plants by the homologous recombination pathway. Failure to repair double-strand breaks and other DNA damages in somatic cells by
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
can lead to cell dysfunction or death, and when failure occurs during
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
, it can cause loss of gametes. The genome sequence of ''P. patens'' has revealed the presence of numerous genes that encode proteins necessary for repair of DNA damages by homologous recombination and by other pathways. PpRAD51, a protein at the core of the homologous recombination repair reaction, is required to preserve genome integrity in ''P. patens''. Loss of PpRAD51 causes marked hypersensitivity to the double-strand break-inducing agent
bleomycin -13- (1''H''-imidazol-5-yl)methyl9-hydroxy-5- 1''R'')-1-hydroxyethyl8,10-dimethyl-4,7,12,15-tetraoxo-3,6,11,14-tetraazapentadec-1-yl}-2,4'-bi-1,3-thiazol-4-yl)carbonyl]amino}propyl)(dimethyl)sulfonium , chemical_formula = , C=55 , H=84 , N=1 ...
, indicating that homologous recombination is used for repair of somatic cell DNA damages. PpRAD51 is also essential for resistance to ionizing radiation. The DNA mismatch repair protein PpMSH2 is a central component of the ''P. patens'' mismatch repair pathway that targets base pair mismatches arising during homologous recombination. The ''PpMsh2'' gene is necessary in ''P. patens'' to preserve genome integrity. Genes ''Ppmre11'' and ''Pprad50'' of ''P. patens'' encode components of the MRN complex, the principal sensor of DNA double-strand breaks. These genes are necessary for accurate homologous recombinational repair of DNA damages in ''P. patens''. Mutant plants defective in either ''Ppmre11'' or ''Pprad50'' exhibit severely restricted growth and development (possibly reflecting accelerated senescence), and enhanced sensitivity to UV-B and bleomycin-induced DNA damage compared to wild-type plants. Image:Physcomitrella Sporophyt.JPG, Cleistocarpous
sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...
of the moss ''P. patens'' Image:Physcomitrella growing on agar plates.jpg, ''P. patens'' plants growing
axenic In biology, axenic (, ) describes the state of a culture in which only a single species, variety, or strain of organism is present and entirely free of all other contaminating organisms. The earliest axenic cultures were of bacteria or unicellul ...
ally ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'' on
agar plate An agar plate is a Petri dish that contains a growth medium solidified with agar, used to culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics. Individual microorganisms placed on the plate wil ...
s (
Petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...
, 9 cm diameter) Image:Bioreaktor quer2.jpg,
Moss bioreactor A moss bioreactor with '' Physcomitrella patens'' A moss bioreactor is a photobioreactor used for the cultivation and propagation of mosses. It is usually used in molecular farming for the production of recombinant protein using transgenic moss. ...
with ''P. patens'' Image:Ecotypes_of_Physcomitrella_patens.JPG, Four different
ecotype In evolutionary ecology, an ecotype,Greek: ''οίκος'' = home and ''τύπος'' = type, coined by Göte Turesson in 1922 sometimes called ecospecies, describes a genetically distinct geographic variety, population, or race within a specie ...
s of ''P. patens'' stored at the International Moss Stock Center Image:Physcomitrella Protonema.jpg,
Protonema A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses. When a moss first grows from a spore, it starts as a ''germ tube'', ...
cells of ''P. patens'' Image:DEV035048A.jpg, The polycomb gene ''FIE'' is expressed (blue) in unfertilised egg cells of the moss ''P. 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. Image: Physcomitrella_knockout_mutants.JPG, ''Physcomitrella'' knockout mutants: Deviating phenotypes induced by transformation with a gene-disruption-library. ''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) are shown. A: Haploid wild-type moss plant completely covered with leafy gametophores and close-up of wild-type leaf. B–D: Different mutants.


Taxonomy

''P. patens'' was first described by
Johann Hedwig Johann Hedwig (8 December 1730 – 18 February 1799), also styled as Johannes Hedwig, was a German botanist notable for his studies of mosses. He is sometimes called the "father of bryology". He is known for his particular observations of sexual r ...
in his 1801 work ', under the name ''Phascum patens''. ''Physcomitrella'' is sometimes treated as a
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
of the genus '' Aphanorrhegma'', in which case ''P. patens'' is known as ''Aphanorrhegma patens''. In: Knight ''et al.'' (2009). The generic name ''Physcomitrella'' implies a resemblance to '' Physcomitrium'', which is named for its large calyptra, unlike that of ''Physcomitrella''. In 2019 it was proposed that the correct name for this moss is ''Physcomitrium patens''.


References


Further reading

*


External links


cosmoss.org - moss transcriptome and genome resource
includin
genome browser

The Japanese ''Physcomitrella'' transcriptome resource (Physcobase)

The NCBI ''Physcomitrella patens'' genome project page




* ttps://web.archive.org/web/20140831112857/http://www.bio-pro.de/magazin/wirtschaft/index.html?lang=en&artikelid=%2Fartikel%2F05167%2Findex.html A small moss turns professional
''Physcomitrella patens'' facts, developmental stages, organs at GeoChemBio
{{Taxonbar, from=Q1645541 Plant models Funariales Plants described in 1801 Taxa named by Philipp Bruch