The moss Physcomitrella patens is the first non-flowering land plant to be selected for genome sequence analysis and the first-draft genome sequence has recently been published. Occupying a basal position in the land plant phylogeny its genome represents a “missing link” between those of the green alga Chlamydomonas and the flowering plant Arabidopsis thaliana, and thus provides an excellent model for comparative studies of the evolution of plant gene function.
This laboratory initiated the acquisition of EST sequence data through the BBSRC-supported Physcomitrella EST Programme (PEP) and we now are establishing a resource for forward genetic interrogation of Physcomitrella by constructing a genetic linkage map densely populated with molecular-markers anchored to the genome sequence. This work has been supported by the Gatsby Charitable Foundation and BBSRC.
Physcomitrella, a simple plant, provides an excellent model system for the study of plant development at the cellular level, and for understanding the evolution of gene function. A unique feature of Physcomitrella is its ability to incorporate transforming DNA by homologous recombination, and we use high efficiency gene targeting to create highly specific gene knockouts - a powerful tool for "reverse genetics". This technology is routinely performed by yeast geneticists, but is not applicable to higher plants that lack the capacity for high frequency gene targeting.
We have recently determined the parameters for optimal gene targeting efficiency, and our next priority is to identify the mechanism of the gene targeting process: Physcomitrella is uniquely suited for an investigation of homologous recombination in plants, by contrast with higher plant models that are generally incompetent in this respect.
We are also interested in plant responses to environmental stress, following our earlier work on cereal embryo development. In cereals, we have studied the switch in the developmental programme between embryonic maturation and germination, focusing on genes encoding Late Embryogenesis Abundant ("LEA") proteins of which the most prominent is the wheat "Em" (Embryonic Maturation) protein - these genes are ABA-regulated and thought to be associated with the acquisition of desiccation tolerance by dormant embryos.
These genes are highly conserved in evolution, and their ABA- and drought-stress induction is conserved in Physcomitrella. Because many mosses exhibit high levels of vegetative desiccation tolerance - a feature associated with the successful colonisation of land by plants approximately 450 million years ago - we are using Physcomitrella as a model system in which to study this process, and the evolution of its regulation.