Though mosses and vascular plants have diverged for more than 400 million years, they share common genetic and physiological processes. A comparative study between representatives of these two lineages can provide insight into the evolutionary mechanisms that have led to the complex structure of modern plants. Thus, the moss Physcomitrella patens (P. patens) is used today as a model organism.
P. patens is one of the few known multicellular organisms with a high rate of homologous recombination. This property enables targeted transgenesis: insertion of an exogenous DNA sequence at a specific position in the genome. Targeted transgenesis, in addition to genetic and genomic comparative studies, provides an opportunity to elucidate the function of specific genes in the development and evolution of plants. Finally, P. patens is increasingly used in biotechnological research, to identify genes to increase crop yields or improve human health.
Similar to all mosses, P. patens life cycle features two alternating generations: an haploid gametophyte producing gametes and a diploid sporophyte producing haploid spores. Spores develop into a filamentous structure (protonema) made of a chloroplast rich chloroneme and a fast-growing caulonema. Protonema filamentous structure develop by growth of their apical cells and can also develop branches from their subapical cells. Instead of producing secondary branches, some of these cells may acquire the ability to produce gametophores, leafy stems anchored to the ground by rhizoids and carrying the sexual organs: the archegone (female) and antheridia (male).
P. patens is monoecious: the female and male organs are both found on the same plant. In water, sperm can swim from the antheridia to the archaegon and fertilize an oocyte. The resulting zygote produces a sporophyte that will produce thousands of spores by meiosis.
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