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The moss Physcomitrella patens is a model for the study of plant cell biology and, by virtue of its basal position in land plant phylogeny, for comparative analysis of the evolution of plant gene function and development. It is ideally suited for 'reverse genetic' analysis by virtue of its outstanding ability to undertake targeted transgene integration by homologous recombination. However, gene identification through mutagenesis and map-based cloning has hitherto not been possible, due to the lack of a genetic linkage map. Using molecular markers [amplified fragment length polymorphisms (AFLP) and simple sequence repeats (SSR)] we have generated genetic linkage maps for Physcomitrella. One hundred and seventy-nine gene-specific SSR markers were mapped in 46 linkage groups, and 1574 polymorphic AFLP markers were identified. Integrating the SSR- and AFLP-based maps generated 31 linkage groups comprising 1420 markers. Anchorage of the integrated linkage map with gene-specific SSR markers coupled with computational prediction of AFLP loci has enabled its correspondence with the newly sequenced Physcomitrella genome. The generation of a linkage map densely populated with molecular markers and anchored to the genome sequence now provides a resource for forward genetic interrogation of the organism and for the development of a pipeline for the map-based cloning of Physcomitrella genes. This will radically enhance the potential of Physcomitrella for determining how gene function has evolved for the acquisition of complex developmental strategies within the plant kingdom.

The recessive mutation of the def gene of pea (Pisum sativum L.) leads to the loss of the hilum, the abscission zone between the seed and the pod. Thereby, it reduces the free dispersal of the seeds through pod shattering. As a prerequisite for a gene isolation via a map-based cloning approach, bulked segregant analysis followed by single plant analyses of over 200 homozygous individuals of a population of 476 F2 plants derived from a cross between 'DGV' (def wild-type) and 'PF' (def mutant), were used to detect markers closely linked to the def locus. The AFLP technique in combination with silver staining was used to maximize numbers of reproducible marker loci. Fifteen AFLP loci showed a genetic distance less than 5 and two of them less than 1 centiMorgans (cM) to the gene of interest. AFLPs were converted into sequence tagged sites (STSs) and into a newly refined AFLP-based single locus marker named the 'sequence specified AFLP' (ssAFLP).