Physcomitrella patens is a moss and an early colonist of exposed earth around the edges of water. It used as a model organism for plant development, physiology and evolution. P. patens is a good model organism because it shares many fundamental physiological and genetic processes with vascular plants. P. patens also has very efficient homologous recombination that allows it to be studied via reverse genetics or gene knockout experiments. In addition to this, the entire genome of P. patens has been completely sequenced, and mutants are readily available, thus making Physcomitrella patens an excellent model organism.
Physcomitrella patens, like all mosses, goes through an alternation of generations between the haploid gametophyte and diploid sporophyte generations. The haploid gametophyte is responsible for producing gametes, while the diploid sporophyte produces haploid spores. The spore then develops into a protonema that is composed of chloronema cells with a large amount of chloroplasts and fast growing caulonema cells. The protonema then develops buds that gives rise to gametophores that contain leafy structures as well as sexual organs.
Proper development of Physcomitrella patens relies on proper function of the genes listed below
Auxin/Cytokinin (Ashton et al, 1979)
- Play important and interdependent roles in several steps of gametophytic development
- Auxin is required for normal caulonemal development
- Cytokinin and Auxin are required for inhibition of the development of secondary chloronema
- Mutants show many more chloronemata than normal and do not develop gametophores
ARPC4 (Perroud et al, 2006)
- Has a role in tip growth and alignment of the polar axis in filaments
- Essential to rapid extension of caulonemal and rhizoid filaments
- Responsible for proper response of tip to polarized light
- Mutant gametophores fail to elongate and distinctive characteristics between caulonema and chloronema filamentous cells are absent
KNOX (Sakakibara et al, 2008)
- Essential to the function of the indeterminate apical meristem
- Function in the diploid organ but not in the haploid indeterminate meristem
- Regulate the frequency of cell division and growth in the diploid determinate meristem
FLO/LFY (Tanahashi et al, 2005)
- 2 genes, PpLFY1 and PpLFY2 play roles in controlling the first zygotic division
- Mutants show mostly normal organogenesis but abnormalities in the pattern of cell division
- Mutants also have a substantially lower number of gametophores that form a sporophyte
- Zygotes in double mutants to not progress to the first cell division
Sakakibara, Keiko., et al.. “Involvement of auxin and a homeodomain-leucine zipper I gene in rhizoid development of the moss Physcomitrella patens.”Development. (2003): 4835-4846. Web. 3 Apr. 2014. <http://dev.biologists.org/content/130/20/4835.short>.
Reski, Ralf. “Molecular Genetics of Physcomitrella.”Planta. 208.3 (1999): 301-309. Web. 3 Apr. 2014. <http://link.springer.com/article/10.1007/s004250050563?LI=true>.
“Physcomitrella patens, moss.” GeoChemBio.com. Nemose, 18 May 2013. Web. 3 Apr 2014. <http://www.geochembio.com/biology/organisms/physcomitrella/
Schaefer, Didier, et al.. “Efficient gene targeting in the moss, Physcomitrella patens.” Plant Journal. 11.6 (2002): 1195-1206. Web. 3 Apr. 2014. <http://onlinelibrary.wiley.com/doi/10.1046/j.1365-313X.1997.11061195.x/abstract>.
Sakakibara, Keiko, et al.. “Class 1 KNOX genes are not involved in shoot development in the moss Physcomitrella patens but do function in sporophyte development.”Evolution & Development. 10.5 (2008): 555-566. Web. 3 Apr. 2014. <http://onlinelibrary.wiley.com/doi/10.1111/j.1525-142X.2008.00271.x/full>.
Tanahashi, Takako, et al.. “Diversification of gene function: homologs of the floral regulator FLO/LFY control the first zygotic cell division in the moss Physcomitrella patens.” Development. (2005): 1727-1736. Web. 3 Apr. 2014. <http://dev.biologists.org/content/132/7/1727.short>.
Ashton, N.W. “Analysis of gametophytic development in the moss, Physcomitrella patens, using auxin and cytokinin resistant mutants.” Planta. 144.5 (1979): 427-435. Print. <http://link.springer.com/article/10.1007/BF00380118>.
Perroud, Pierre-François. “The role of ARPC4 in tip growth and alignment of the polar axis in filaments of Physcomitrella patens.” Cytoskeleton. 63.3 (2006): 162-171. Web. 3 Apr. 2014. <http://onlinelibrary.wiley.com/doi/10.1002/cm.20114/abstract>.