The moss, Physcomitrella patens

The tractability of the moss, Physcomitrella patens, to genetic analysis and the accessibility of its living tissues to direct observation make this species an extremely attractive system for studying plant development. The gametophyte generation, being haploid, allows direct detection of mutant phenotypes. The protonemal stage of gametophyte development is composed of cell filaments that facilitate detailed study of cell polarity and pattern determination. Techniques for the molecular analysis of gene expression include transformation, using either poly ethylene glycol mediated uptake of DNA by protoplasts or biolistic delivery into protonemal tissue. When transforming DNA contains sequences homologous to genomic sequences, recombination can occur with high frequency, providing a way not only for the directed inactivation of genes, but also for precise allele replacement. Further development of the system is required, and priorities include the establishment of a gene tagging system. Other moss species have different advantages and a further priority must be the extension of the techniques devised for Physcomitrella to other moss species.