Rudolf Hagemann

RNA editing in tobacco chloroplasts leads to the formation of a translatable psbL mRNA by a C to U substitution within the initiation codon

The psbL gene which codes for a 38 amino acid peptide of photosystem II, together with the photosynthetic genes psbE and psbF, is contained in a conserved position of many species of higher plant plastomes. The alignment of the psbL nucleotide sequences from ten species shows strong conservation, which is indicative of a functional gene. The tobacco and spinach psbL genes have, however, an ACG codon instead of the initiator ATG codon observed in the homologous position of the other eight species. Evidence is presented that in tobacco chloroplasts a translatable psbL mRNA containing an AUG initiator codon is formed by a C to U editing of the ACG codon. This observation, following the previously reported editing of an rpl2 gene in maize chloroplasts, underlines a more widespread occurrence of this type of posttranscriptional mRNA modification and demonstrates its presence in a dicotyledon plant.

Variations of chloroplast DNAs in the genus Pelargonium and their biparental inheritance.

SummaryThe comparison of EcoRI patterns of chloroplast DNAs (ctDNAs) from five species of the genus Pelargonium and from 16 cultivars and varieties of Pelargoniumzonale hort. demonstrates a remarkable inter- and intraspecific ctDNA (plastome) variation. The plastome of the P. zonale varieties could be differentiated into groups I, II and III. Reasons for this variation seem to be: occurrence of numerous spontaneous plastome mutations, intense hybridisation by gardeners and breeders, and biparental plastid inheritance.Crosses of P. zonale varieties with different ctDNA types lead to the direct evidence on the molecular level of biparental plastid inheritance and plastid sorting-out in F1-hybrids.

Tissue- and stage-specific modulation of RNA editing of the psbF and psbL transcript from spinach plastids — a new regulatory mechanism?

The psbE operon of spinach chloroplasts, which includes the genes psbE, psbF, psbL and psbJ, encodes two RNA editing sites. One site corresponds to the initiation codon of the psbL transcript, as has been described earlier for the homologous transcript from tobacco, while at a second editing site, newly reported here, an internal phenylalanine codon of the psbF transcript is restored. Both these sites were investigated with respect to the extent of editing in spinach plastids at various developmental stages. The apparent existence of only completely edited transcripts in etioplasts and chloroplasts, indicates that light-induced processes are not acting as determinants in eliciting the editing process. Reduced editing is, however, observed in the psbF and psbL transcript from seeds and roots. This finding suggests that the RNA editing process is differentially down-regulated in leucoplasts and proplastids and that editing may, therefore, function as a regulatory device in lastid gene expression.

Plastid Genetics in Higher Plants

In the first decade after the rediscovery of the Mendelian laws already some traits of non-Mendelian heredity were described. These were chlorophyll deficiencies of dicotyledons, the inheritance of which was analysed by Erwin Baur in Pelargonium zonale (1909) and Antirrhinum majus (1910) and by Carl Correns (1909) in Mirabilis jalapa. With this, the existence of two modes of plastid inheritance had been found, viz. biparental and uniparental maternal plastid inheritance. Only many decades later, hints were obtained at cases of uniparental paternal plastid inheritance in gymnosperms and possibly in angiosperms.

The foundation of extranuclear inheritance: plastid and mitochondrial genetics.

In 1909 two papers by Correns and by Baur published in volume 1 of Zeitschrift für induktive Abstammungs- und Vererbungslehre (now Molecular Genetics and Genomics) reported on the non-Mendelian inheritance of chlorophyll deficiencies. These papers, reporting the very first cases of extranuclear inheritance, laid the foundation for a new field: non-Mendelian or extranuclear genetics. Correns observed a purely maternal inheritance (in Mirabilis), whereas Baur found a biparental inheritance (in Pelargonium). Correns suspected the non-Mendelian factors in the cytoplasm, while Baur believed that the plastids carry these extranuclear factors. In the following years, Baur’s hypothesis was proved to be correct. Baur subsequently developed the theory of plastid inheritance. In many genera the plastids are transmitted only uniparentally by the mother, while in a few genera there is a biparental plastid inheritance. Commonly there is random sorting of plastids during ontogenetic development. Renner and Schwemmle as well as geneticists in other countries added additional details to this theory. Pioneering studies on mitochondrial inheritance in yeast started in 1949 in the group of Ephrussi and Slonimski; respiration-deficient cells (petites in yeast, poky in Neurospora) were demonstrated to be due to mitochondrial mutations. Electron microscopical and biochemical studies (1962–1964) showed that plastids and mitochondria contain organelle-specific DNA molecules. These findings laid the molecular basis for the two branches of extranuclear inheritance: plastid and mitochondrial genetics.

Comparative restriction endonuclease analysis and molecular cloning of plastid DNAs from wild species and cultivated varieties of the genus Beta (L.).

SummaryA phyletic tree of the genus Beta has been constructed based on EcoRI and PstI plastid DNA restriction patterns of eight species from three sections of the genus. In contrast to the remarkable morphological variability of the varieties of B. vulgaris the restriction patterns of the plastid DNA of this species were found to be almost identical. The comparison of plastic DNAs of B. vulgaris crassa fertile and sterile lines with 13 different restriction enzymes revealed only a single fragment polymorphism in the HindIII patterns. Hybridization analyses in the plastidal rDNA region revealed an interesting loss of an EcoRI restriction site in all cultivated B. vulgaris varieties in contrast to wild species. The results of the construction of clone banks for SalI and BamHI fragments of plastid DNA from fertile B. vulgaris crassa are reported and difficulties in the cloning of specific fragments are discussed.

Extranuclear Inheritance: Plastid Genetics: Manipulation of Plastid Genomes and Biotechnological Applications

When Erwin Baur, at the beginning of this century, proposed that the non-Mendelian inheritance of leaf variegations can be explained with the assumption that chloroplasts (plastids) contain their own genetic information (Baur 1909, 1910), he found himself confronted with the sheer disbelief of many of his colleagues (Hagemann 1999). It took more than half a century until the discovery of chloroplast DNA (Chun et al. 1963; Sager and Ishida 1963) provided the ultimate proof for Baur’s ingenious hypothesis. Already with the very first analyses on chloroplast DNA sequences, it became obvious that plastid and eubacterial genomes are evolutionarily related (Schwarz and Kossel 1979, 1980), a finding that provided direct molecular evidence for the endosymbiotic origin of organelles (Gray 1989). The elucidation of the complete DNA sequence of two chloroplast genomes in 1986 (Ohyama et al. 1986; Shinozaki et al. 1986) marks a milestone in organelle genetics and has had a profound influence on our understanding of the biology and evolution of plastids (cf. Hagemann and Hagemann 1994; Hagemann et al. 1996, 1998).

Paramutation at the sulfurea locus of Lycopersicon esculentum Mill. : VII. Determination of the time of occurrence of paramutation by the quantitative evaluation of the variegation.

Summary1.In tomato plants heterozygous for a mutant allele of the sulfurea (sulf) locus paramutation may take place: under the influence of a paramutant sulf allele, the paramutable wild type allele sulf+, which is present in the same nucleus, is heritably altered with a definite frequency to a sulf mutant allele, either of the sulfpuraor the sulfvaggroup.2.A number of the sulf+sulf heterozygotes remain entirely green during their whole ontogenetic development (type I plants, without paramutation). However, others of the plants become variegated: these variegated plants contain-apart from green sectors — only yellow-green speckled sulfvagsectors (type II plants), or only pure yellow sulfpurasectors (type III plants) or both sulfvagand sulfpurasectors side by side (type IV plants).3.For all variegated plants (types II, III and IV) we determined the sizes of the green and of the paramutant sulfvagand sulfpurasectors and made a statistical analysis of the values obtained.4.We conducted observations over a period of three years and obtained following findings: type II plants (with sulfvagsectors) have an average size of the paramutant sectors of 27.9% (the whole plant being 100%). Type III plants (with sulfpurasectors) have an average sectors size of 25.7%, whereas the size of the paramutant sectors in type IV plants (with both sulfvagand sulfpurasectors) amounts to 54.4% (35.7% sulfvagand 18.7% sulfpura). Thus, the occurrence of tissues of both phenotypes in one plant has, on the average, been found to be correlated with a doubling of the proportion of paramutant sectors in that plant.5.Within sulf+sulf heterozygotes there is, in general, a positive correlation between the frequency of paramutant plants and the proportion of paramutant sectors within the plants. This is mainly due to the fact that there is a significant positive correlation between the frequency of type IV plants and the frequency of paramutant plants, i.e. the more plants within a progeny variegated, the greater the frequency of type IV plants containing both sulfvagand sulfpurasectors.6.These findings (mathematically analysed and compared with the consequences of several models) may result in the following concept: the paramutation processes in sulf+sulf heterozygotes are restricted to a small group of cells (16 cells at the most) during a short period of about three cell generations after seed germination and expansion of the cotyledons. In the course of which, the probability for the occurrence of paramutation decreases rather quickly from one cell generation to the next. These characteristics of paramutation processes mentioned cause the occurrence of rather large and well defined sectors of paramutant tissue.

Biosynthesis of Thylakoids and the Membrane-Bound Enzyme Systems of Photosynthesis

The chloroplasts are the sites of photosynthesis in eukaryotic plant cells. Within these organelles the processes of photosynthetic energy uptake, transfer, and transformation take place in the thylakoids. In this article we wish to describe characteristics of the thylakoids and of the membrane-bound enzyme systems, their biosynthesis, and especially the cooperation of nuclear DNA and plastid DNA and of the protein-synthesizing systems in the cytoplasm and in the plastid during the ontogenetic development of the chloroplast.

Paramutation (somatic conversion) at the Sulfurea locus of Lycopersicon esculentum V. The localisation of Sulf

Paramutation (somatic conversion) at the Sulfurea locus of Lycopersicon esculentum V. The localisation of Sulf