Integrating the genome sequence and genetic linkage map of Physcomitrella patens: a platform for map based gene cloning

点击翻译按钮获取中文摘要

Our research: BBSRC support of Leeds University over a period of 30 years has led us to pioneer the establishment of the moss Physcomitrella patens as an internationally adopted 'model organism' for the study of plant cell and developmental biology. This support enabled us to (i) develop techniques for the isolation of mutants aberrant in basic plant processes - the first step to identify the genetic basis of biological processes (ii) optimise a technique for genetic engineering by 'gene targeting' - a precision tool not possible in any other plant (iii) initiate a programme of gene discovery that has culminated in the complete sequencing of the Physcomitrella genome by an international consortium. Now we shall establish the final tool to enable the rapid and routine identification of genes that underlie abnormal mutants: the integration of the Physcomitrella genome sequence with its genetic linkage map. This will enable the international and UK plant science community to extract maximum value from the newly released Physcomitrella genome through the application of 'comparative functional genomics' - a BBSRC research priority. The value of comparative studies: Our understanding of complex biological processes has been revolutionised by genetic experiments conducted using a small number of well characterised model organisms. In the Animal Kingdom, the study of the nematode worm, the fruit fly, the zebra fish and the mouse allows analysis of animal development across a wide evolutionary spectrum encompassing increasing levels of complexity. Such wide comparative analysis enables us to discern the evolutionary processes that have generated these disparate creatures, and the ways in which essentially similar genes have been differently utilised in the course of evolution. Within the Plant Kingdom, the comparable model organisms that allow a similarly wide evolutionary perspective to be achieved are the flowering plant, Arabidopsis thaliana, and the moss, Physcomitrella patens. Model organisms are chosen for their experimental tractability. All these organisms have had their whole genome sequences determined. All can be manipulated by the introduction of foreign DNA: in the case of the mouse and the moss, foreign DNA can be introduced to specific sites within their genomes with exquisite precision. In all these organisms, random mutations can be induced that cause radical defects in their normal developmental processes. By identifying the genes in which such mutations have occurred, we identify the genes that normally regulate these processes. This identification is possible only where the sequenced genome is supported by a 'genetic linkage map': a representation of the genome based on the inheritance of large numbers of mutations in a large population. Mutations that lie in adjacent sections of the genome are typically inherited together, and are said to be 'genetically linked'. A gene that is responsible for a mutant trait can be isolated if that trait is co-inherited (genetically linked) with neighbouring, known 'genetic markers' - typically lengths of DNA whose sequence is known. This potent experimental approach allows the functional identification of genes without prior knowledge of their sequence. Such an approach is routine in Arabidopsis. This proposal will make it routine in Physcomitrella and accessible to all plant scientists. Physcomitrella is not a flowering plant. It is a member of the earliest group of land plants - the bryophytes - an ancient and biodiverse group which emerged ca. 300 million years before the flowering plants. It therefore represents an ancestral reference by which divergence in plant gene structure and function has occurred. It also provides insights into 'primitive' plant traits such as enhanced dehydration tolerance (essential for a successful colonisation of the land) and the origins of plant multicellularity, that retain their value for future plant improvement.