Malformation of gynoecia impedes fertilisation in bud-flowering Calluna vulgaris.

In Calluna vulgaris, a common bedding plant during autumn in the northern hemisphere, the bud-blooming mutation of flower morphology is of high economic importance. Breeding of new bud-blooming cultivars suffers from poor seed set in some of the desirable bud-flowering crossing partners. In the current study, fertilisation and seed development in genotypes with good or poor seed set were monitored in detail in order to examine pre- and post-zygotic cross breeding incompatibilities. Whereas no distinct differences were detected in seed development, pollen tube growth was impeded in the pistils of genotypes characterised by poor seed set. Detailed microscopic analysis revealed malformations of the gynoecia due to imperfect fusion of carpels. Hence, a pre-zygotic mechanism hindering pollen tube growth due to malformation of gynoecia was deduced. An interaction of putative candidate genes involved in malformation of gynoecia with floral organ identity genes controlling the flower architecture is discussed.

Comparative analysis of cell cycle events in zygotic and somatic embryos of Cyclamen persicum indicates strong resemblance of somatic embryos to recalcitrant seeds.

Embryo development and germination of Cyclamen persicum have been comparatively characterized for zygotic and somatic embryos with regard to mitotic activity and morphology in order to identify developmental abnormalities in somatic embryogenesis. Zygotic embryo development proved to be highly synchronous with distinct periods of cell division, cell elongation and embryo maturation within a total period of 17 weeks of seed development. Somatic embryo development was accomplished within only 3 weeks, resulting in a mixture of morphologically highly variable embryos. No distinct developmental periods could be identified and no reduction of the mitotic activity was discovered for non-desiccated somatic embryos. Controlled desiccation of somatic embryos severely reduced their germination rate, demonstrating resemblance of somatic embryos to recalcitrant seeds, whereas zygotic Cyclamen seeds could be characterized as typically orthodox.

Large-scale analysis of 73 329 physcomitrella plants transformed with different gene disruption libraries: production parameters and mutant phenotypes.

Gene targeting in the moss Physcomitrella patens has created a new platform for plant functional genomics. We produced a mutant collection of 73 329 Physcomitrella plants and evaluated the phenotype of each transformant in comparison to wild type Physcomitrella. Production parameters and morphological changes in 16 categories, such as plant structure, colour, coverage with gametophores, cell shape, etc., were listed and all data were compiled in a database (mossDB). Our mutant collection consists of at least 1804 auxotrophic mutants which showed growth defects on minimal Knop medium but were rescued on supplemented medium. 8129 haploid and 11 068 polyploid transformants had morphological alterations. 9 % of the haploid transformants had deviations in the leaf shape, 7 % developed less gametophores or had a different leaf cell shape. Other morphological deviations in plant structure, colour, and uniformity of leaves on a moss colony were less frequently observed. Preculture conditions of the plant material and the cDNA library (representing genes from either protonema, gametophore or sporophyte tissue) used to transform Physcomitrella had an effect on the number of transformants per transformation. We found correlations between ploidy level and plant morphology and growth rate on Knop medium. In haploid transformants correlations between the percentage of plants with specific phenotypes and the cDNA library used for transformation were detected. The number of different cDNAs present during transformation had no effect on the number of transformants per transformation, but it had an effect on the overall percentage of plants with phenotypic deviations. We conclude that by linking incoming molecular, proteome, and metabolome data of the transformants in the future, the database mossDB will be a valuable biological resource for systems biology.

A tool for understanding homologous recombination in plants.

Attempts for establishing an efficient gene targeting (GT) system in seed plants have hitherto not been successful. In contrast, GT based on homologous recombination is highly efficient in Physcomitrella, making this moss a novel tool in reverse genetics. However, why homologous and illegitimate recombination are differently regulated between Physcomitrella and seed plants is still enigmatic. Here we update the state of the art of GT in Physcomitrella and discuss approaches to unravel this enigma. Identification of molecular factors significantly enhancing GT and their subsequent transfer to crop plants will have a great impact on plant biotechnology by enabling precise genetic engineering. Physcomitrella appears to be the most useful model system in this context.