Cytoplasmic inheritance of chloroplast coupling factor 1 subunits

An analysis of interspecific hybrids of Nicotiana spp. in which one of the parents was sensitive to tentoxin showed that this sensitivity was transmitted only through the female parent. Since tentoxin acts by selectively binding to the alpha,beta subunit complex of chloroplast coupling factor 1, the gene(s) specifying either one or both of these subunits is located in the cytoplasm.     

Effect of tagetitoxin on the levels of ribulose 1,5-bisphosphate carboxylase, ribosomes, and RNA in plastids of wheat leaves

Growth of wheat seedlings in the presence of the phytotoxin tagetitoxin produces pigment-deficient leaves of normal size and morphology whose cells contain only rudimentary plastids. We could not detect the accumulation of either the plastid-encoded large subunit or the nuclear-encoded small subunit of the chloroplast stromal enzyme ribulose 1,5-bisphosphate carboxylase (RuBPCase) in western blots of protein extracted from leaves of such seedlings. Sucrose gradient centrifugation profiles showed that plastid ribosomes were essentially absent in toxin-treated leaf tissue while cytoplasmic ribosomes were relatively unaffected. Northern blot analysis of RNA in toxin-treated leaves showed a deficiency of plastid ribosomal RNA (16S and 23S) as well as reduced levels of plastid mRNAs for the large subunit of RuBPCase and for the 32 kilodalton thylakoid Q_B polypeptide. Northern analysis also showed that the nuclear-encoded rbcS mRNA for the small subunit of RuBPCase is present in only trace amounts in toxin-treated leaves.     

Characterization of GATA/GACA-related sequences on proximal chromosome 17 of the mouse

Chromosome behaviour during meiosis in male Syrian hamsters heterozygous for one of three translocations was analysed as part of a study of the transmission of these structural changes. Synapsis was studied using preparations of synaptonemal complexes, and chiasmate associations and the results of anaphase I segregation were studied in air-dried preparations of metaphases I and II respectively. The main findings were: (i) that, at least in the two trivalent-forming translocations, there is no simple relationship between either the frequency or the extent of synapsis and chiasma formation between the chromosomes involved in the translocation; (ii) that the presence of a univalent in a substantial proportion of metaphase I cells does not necessarily lead to irregular segregation as judged by analysis of metaphase IIs; and (iii) conversely, that in translocation heterozyotes in which metaphase I contains the chromosomes involved in the translocation as a quadrivalent or as two bivalents, with no univalents or trivalents, unexpected numerical segregation can be found. The observations of meiotic chromosomes behaviour reported here show that it is not always possible to predict the effects of structural change, or to determine the basis of these effects, from an analysis of any stage of meiosis taken in isolation, or from an analysis of an apparently similar change.     

Image analysis of restriction enzyme fingerprint autoradiograms

A genome mapping system has been developed that reads and assemblesdata from clones analysed by restriction enzyme fragmentationand polyacrylamide gel electrophoresis. Input data for the systemcan be most effectively obtained by the use of a scanning densitometerand image-processing package, such as that described in thisarticle. The image-processing procedure involves preliminarylocation of bands, cooperative tracking of lanes by correlationof adjacent bands, a precise densitometric pass, alignment ofthe marker bands with the standard, optional interactive editing,and normalization of the accepted bands. Received on August 31, 1988; accepted on December 6, 1988     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

Nucleotide polymorphism in the chalcone synthase-A locus and evolution of the chalcone synthase multigene family of common morning glory Ipomoea purpurea

Chalcone synthase (CHS) is a small multigene family with at least four members (CHS-A, B, C and PS) in common morning glory Ipomoea purpurea ROTH. The chalcone synthase enzyme performs the initial condensation reaction that results in the 15-carbon three-ring structure that is the backbone of flavonoid biosynthesis. The biochemical pathway that commences with CHS is important in plant disease defence, pigment biosynthesis and UV protection. Accordingly, it is of substantial interest to characterize levels and patterns of molecular diversity for genes that encode this important enzyme. We report the sequence of 19 CHS-A alleles from Mexican and American populations of common morning glory. American populations of this annual self-compatible vine are believed to have been introduced from Mexico, where the species is native. Individual plants were sampled from populations of common morning glory throughout Mexico and the south-eastern USA. Four American alleles were sequenced and these, together with one allele from Mexico City, were identical in primary nucleotide sequence. These data suggest a restricted origin for the American population, probably as a consequence of selection for domestication by pre-Columbian peoples. Additionally the Mitontic (Chiapas, Mexico) population is significantly more homogeneous than expected by chance indicating that this population may also have experienced a recent population bottleneck. Estimates of nucleotide diversity from the Mexican CHS-A alleles were high. We present evidence that these estimates may, in part, result from low to moderate levels of interlocus recombination/gene conversion. We also present evidence that the ancient duplication of the CHS gene family, preceding the origin of the genus Ipomoea, was associated with heterogeneity in the rate of substitution between the resulting gene family members. The group of gene family members whose sequences possess a signature amino acid of the closely related Stilbene synthase exhibit a significantly faster proportional rate of nonsynonymous substitution.     

STUDIES ON THE AUTECOLOGY OF THE MARINE DIATOM THALASSIOSIRA NORDENSKIOELDII. II. THE INFLUENCE OF CELL SIZE ON GROWTH RATE,AND CARBON,NITROGEN, CHLOROPHYLL a AND SILICA CONTENT1

The effect of cell size on growth rates and some cellular contents of Thalassiosira nordenskioeldii Cleve has been measured at 0 and 10 C. At 0 C the growth rate did not vary with cell size. The 2 smallest clones at this temperature had reduced growth rates because of the induction of sexuality in that size range. The clones grown at 10 C showed a significant negative relationship between growth rate and valve diameter with the cell surface area/volume ratio positively related to growth rate. At both temperatures the smaller cells had proportionately more carbon and nitrogen/unit cell volume. The amount of chlorophyll a and silica/unit cell surface area increased with increasing cell surface area at both 0 and 10 C. Both the C/N and C/chl a ratios showed no significant change with cell size at either temperature but there was a significant increase in the C/chl a ratio at 0 C. The C/Si ratio decreased with increasing cell size at both 0 and 10 C.