GENOME ANALYSIS OF THE MOSS PHYSCOMITRELLA PATENS (HEDW) BSG

A wild-type (WT) strain of the moss Physcomirrella patens (Hedw.) B.S. G., two mutants derived from it (PC22 and P24), and a somatic hybrid, PC22(+)P24, were analysed. Staining of metaphases revealed 54 +/- 2 ch romosomes in the somatic hybrid and 27 chromosomes in the wild type an d the two mutants. Using flow cytometry (FCM), DNA contents were calcu lated to be 0.6 pg (WT, PC22), 1.2 pg (P24), and 1.6 pg (PC22(S)P24) p er nucleus, respectively. Southern hybridization provided evidence for at least one family of highly repetitive DNA and, furthermore, reveal ed different amounts of repetitive DNA in the four genotypes. However, these sequences cannot account for the 100% increase in the nuclear D NA amount in mutant P24, relative to wild type. In FCM analyses every moss genotype generated just one single peak of fluorescence, indicati ng an arrest in the cell cycle during the daytime. Thermal denaturatio n of wild-type DNA revealed a G+C content of 34.6% for total DNA and 3 8.6% for plastid DNA. A cDNA library of 1.2 x 10(6) independent clones was established, from which sequences homologous to cab and rbcS, res pectively, were isolated. These genes show significant homologies to t hose of higher plants, and, likewise, comprise multigene families. No restriction fragment length polymorphisms could be detected between th e four moss genotypes using these cDNA probes.