3 The Moss Physcomitrella patens A Novel Model System for Plant Development

The moss Physcomitrella patens has been used as an experimental organism for more than 80 years. Within the last 15 years, its use as a model to explore plant functions has increased enormously. The ability to use gene targeting and RNA interference methods to study gene function, the availability of many tools for comparative and functional genomics (including a sequenced and assem-bled genome, physical and genetic maps, and>250,000 expressed sequence tags), and a dominant haploid phase that allows direct forward genetic analysis have all led to a surge of new activity. P. patens can be easily cul-tured and spends the majority of its life cycl