View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Magazine R261 Developmental mutants have been and include about 24,000 used to investigate the genes and Physcomitrella different living species. mechanisms controlling cell, leaf patens and flower shape, flower A tiny plant, upside-down... All organisation and plant plants develop from single cells. architecture. With studies in Ralf Reski1 and David J. Cove2 In seed plants, these zygotes Arabidopsis and other species, this develop into embryos which work has also begun to reveal the become encapsulated in seeds levels of evolutionary conservation What is Physcomitrella for dispersal. Mosses produce within the flowering plants and patens? A moss which is proving spores not seeds. What makes even outside the plant kingdom. to be a useful new model plant the difference? Plants show an species, one that is increasingly alteration of two generations: What does the future hold for being used in experimental one, the gametophyte, is haploid Antirrhinum research? In studies. and produces sex organs and addition to its continuing role as a gametes — sperm and egg cells genetic model for plant biology What place have mosses in the generated by mitosis. As in and development, several new wider scheme of things? They animals, sperm fertilize egg cells experimental avenues are are plants, though rather different to produce diploid zygotes which beginning to be explored with from the seed plants which subsequently grow into embryos. Antirrhinum. A major challenge in usually come to mind when we These embryos produce the biology is to link variation at the think of plants — the flowering diploid sporophyte generation, molecular level to phenotypes and plants, such as the weed which produces haploid spores to the evolutionary and ecological Arabidopsis, or conifers, such as by meiosis. significance of a trait. the Christmas tree. Mosses do Spores give rise to the next Comparisons of closely related not have flowers, vascular tissue gametophyte generation. In seed taxa can be especially informative or seeds; they are thus grouped plants, the gametophytes are about microevolutionary into a different subdivision of reduced to a few cells which only processes, and Antirrhinum is an plants — of which there are four specialized botanists can find; excellent model for this kind of in total — from the flowering the dominating generation is the analysis. About 18 wild plants. Mosses and liverworts diploid sporophyte. In Antirrhinum species are found in used to be placed in the same bryophytes, including mosses, South-West Europe and Northern phylum, but they are now the dominating generation is the Africa: these display considerable generally regarded as being haploid gametophyte and the variation in these traits, including sufficiently different to be placed sporophyte is a reduced flower colour patterns, flower and in two distinct phyla: Bryophyta structure, which is completely leaf shape and size and plant and Hepatophyta, respectively. dependent on the gametophyte growth habit. Usefully, most of the Mosses have evolved with little (Figure 1). species are interfertile, and so change from the first land plants. So, very early in land plant amenable to genetic analysis. This evolution, a major decision was makes it feasible to identify and made: whether to grow in the isolate genes that underlie species A diploid sporophyte stage, as in differences and to test the seed plants, or in the haploid adaptive importance of traits. gametophyte stage, as in the Antirrhinum is also embracing mosses. This is probably one of the technology age: a virtual the reasons why mosses are too snapdragon project is currently small to be used as Christmas underway. It is hoped that trees. modelling the growth and development of Antirrhinum will So why the interest in provide insight into the patterns B Gametophyte Physcomitrella patens? The and processes underlying plant haploidy of the predominant development. Here’s to the next gametophyte generation in mosses Gametes 150 years of Antirrhinum Meiosis provides technical advantages. In research! haploid organisms, we do not need to be concerned with genetic Zygote Where can I find out more? dominance, as we cannot have http://www.antirrhinum.net Sporophyte heterozygous haploid tissue. As a Schwarz-Sommer, Z., Davies, B. and Current Biology consequence, a loss-of-function Hudson, A. (2003). An everlasting pioneer: the story of Antirrhinum mutation in a gene cannot be research. Nat. Rev. Genet. 4, 657- Figure 1. compensated by a functional allele 666. (A) A Physcomitrella sporophyte devel- on the homologous chromosome, oping on a leafy gametophyte. (B) The Department of Cell and Developmental life cycle of a moss (see text for details). as there is no homologous Biology, John Innes Centre, Colney The photo in (A) was taken by Manuel chromosome in a haploid cell. Lane, Norwich, NR4 7UH, UK. Mildner. Thus, altering or destroying a gene Current Biology Vol 14 No 7 R262 in a haploid organism directly enzymes that mediate plant- leads to an altered phenotype, specific protein glycosylation Theory in Biology making forward and reverse alters the modification patterns of genetic approaches more moss proteins to a human-like straightforward in haploid moss pattern; a milestone in the A precarious than in diploid seed plants. production of biopharmaceuticals A major additional asset of in plants. balance mosses came from the discovery that, in the moss Physcomitrella The best has yet to come... John J. Tyson patens, recombination occurs Sequence information from the between DNA introduced into cells Physcomitrella transcriptome is Many areas of modern science by transfection and homologous rapidly increasing and presently and engineering owe their sequences in its nuclear DNA. This covers more than 95% of the strength and vitality to a rich occurs as efficiently as in yeast — estimated 25,000 protein-encoding interplay of experiment, theory five orders of magnitude (!) more moss genes. Mosses have and computation. For example, efficiently than in any other plant conserved, ancient biochemical quantum chemistry, species that has been tested. pathways; unlike seed plants they aerodynamics, meteorology and Since then, this technique has show no real codon-bias; on membrane electrophysiology are been used to study gene–function average, they have fewer all firmly based on extensive relationships in single gene representative members per quantitative observations, sound knockout mosses. Additionally, protein family; and they have more theoretical formalisms and homologous recombination has than 5,000 genes with no clear accurate, predictive calculations. been used to generate tagged, homolog in seed plants. This Molecular cell biology, on the saturated Physcomitrella mutant impressive set of novel genes is other hand, is still, for the most collections as the basis for attracting more and more part, proudly and precariously genome-wide studies of plant scientists. balanced on one leg — gene functions. However, to fully understand — experimental observations — and and exploit — land plant diversity, its staunchest defenders believe A special offer from moss? The the full genome sequence of that theoretical and computational last common ancestor of mosses Physcomitrella is needed. The approaches have little or nothing and seed plants lived about 450 genome size is 511 Mb on 27 to contribute to our understanding million years ago. Mosses have chromosomes, so sequencing the of cell physiology (see Peter not changed much since then, complete genome is not too Lawrence’s recent essay in these and, consequently, they offer the daunting a mission these days. pages Theoretical embryology: a chance to learn more about plant An international sequencing route to extinction? [1]). evolution and diversity. Are there consortium will be launched at This view is surely wrong. A living differences between the next international moss cell is an intrinsically dynamical gametophytic and sporophytic meeting in Freiburg, Germany system, ceaselessly adapting in gene regulation? How do single (www.plant- space, time and internal state to cells decide to differentiate into biotech.net/moss2004). Support environmental challenges. Catalogs new tissues? Are basic from the broader community, of genes and static diagrams of the mechanisms of regulatory however, is greatly appreciated. structural and functional networks and cross-talk relationships of proteins, though conserved between mosses and Where can I find out more? necessary for full understanding, seed plants? Can novel genes or Cove, D.J. (2000). The moss, can never adequately account for metabolites be identified from Physcomitrella patens. J. Plant the dynamism of organelles and Growth Reg. 19, 275–283. moss? Reski, R. (1998). Development, cells. Take, for example, cilia: these Mosses offer a variety of genetics and molecular biology of beautiful tiny whips, attached to metabolites that are not known mosses. Bot. Acta 111, 1–15. many cells, lash back and forth in from seed plants. Some of them, Schaefer, D.G. (2002). A new moss wondrous synchrony, propelling genetics: targeted mutagenesis in like very long-chain Physcomitrella patens. Annu. Rev. cells through liquids or liquids past polyunsaturated fatty acids, are of Plant Biol. 53, 477–501. cells. Without cilia you wouldn’t significant commercial value in Useful moss links: have been born (they transport improving the human