A reference chromosomal map of the hot chili pepper Capsicum pubescens cv. “locoto” (Solanaceae)

Capsicum pubescens is a cultivated hot chili pepper, consumed in Latin American cuisine as a distinctive ingredient, and popularly known as “locoto” or “rocoto”. This taxon is also an outstanding source of resistance to biotic and abiotic stresses as well as other valuable fruit traits for breeding of the worldwidely cultivated C. annuum and related species. In this study, the chromosome complement of C. pubescens cv. “locoto” (2n = 24) was deeply characterized through a sequential combination of conventional and molecular cytogenetics approaches comprising: Ag-NOR staining, heterochromatic fluorescent C-DAPI, DAPI/AMD-CMA/DA bandings, fluorescence in situ hybridization (FISH) of Capsicum-derived probes of the 5S and 18S-25S rRNA genes and different regions of spacers of the ribosomal unit, as well as telomeric probe. The markers identified were systematically combined with morphological karyotype parameters - number, size, centromeres, satellites - to produce a physical map which allowed the identification of several landmarks in each individual chromosome. The reference chromosomal map of C. pubescens here presented is the most comprehensively developed in Capsicum so far. It is envisioned that this chromosomal map will serve as a reference framework for the upcoming sequencing projects and as starting point to assist future genetic mapping of important agronomic traits.

Isolating Chromosomes of the Komodo Dragon: New Tools for Comparative Mapping and Sequence Assembly

We developed new tools to build a high-quality chromosomal map of the Komodo dragon (Varanus komodoensis) available for cross-species phylogenomic analyses. First, we isolated chromosomes by flow sorting and determined the chromosome content of each flow karyotype peak by FISH. We then isolated additional Komodo dragon chromosomes by microdissection and amplified chromosome-specific DNA pools. The chromosome-specific DNA pools can be sequenced, assembled, and mapped by next-generation sequencing technology. The chromosome-specific paint probes can be used to investigate karyotype evolution through cross-species chromosome painting. Overall, the set of chromosome-specific DNA pools of V. komodoensis provides new tools for detailed phylogenomic analyses of Varanidae and squamates in general.

Cytotaxonomy of Simulium (Montisimulium) ghoomense (Diptera: Simuliidae) from the Darjeeling Hills, India

The polytene chromosomes are mapped for a scarce Himalayan simuliid, Simulium (Montisimulium) ghoomense Datta, from the Darjeeling area of India. This species has three tightly paired polytene chromosomes with a haploid number of 3. Chromosomes I, II, and III account for 39.6%, 30.3%, and 30.1% of the total complement length, respectively. The centromeres of chromosomes II and III consistently form a putative partial chromocenter. Sex chromosomes are undifferentiated and polymorphisms and sibling species are lacking in a sample of 35 larvae. This is the first chromosomal map for a species in the subgenus Montisimulium in India.

Chromosomal Map of the Model LegumeLotus japonicus

Lotus japonicus is a model plant for the legume family. To facilitate map-based cloning approaches and genome analysis, we performed an extensive characterization of the chromosome complement of the species. A detailed karyotype of L. japonicus Gifu was built and plasmid and BAC clones, corresponding to genetically mapped markers (see the accompanying article by Sandal et al. 2002, this issue), were used for FISH to correlate genetic and chromosomal maps. Hybridization of DNA clones from 32 different genomic regions enabled the assignment of linkage groups to chromosomes, the comparison between genetic and physical distances throughout the genome, and the partial characterization of different repetitive sequences, including telomeric and centromeric repeats. Additional analysis of L. filicaulis and its F1 hybrid with L. japonicus demonstrated the occurrence of inversions between these closely related species, suggesting that these chromosome rearrangements are early events in speciation of this group.

The Methyl Group of theN6-Methyl-N6-Threonylcarbamoyladenosine in tRNA of Escherichia coli Modestly Improves the Efficiency of the tRNA

ABSTRACT tRNA species that read codons starting with adenosine (A) containN 6-threonylcarbamoyladenosine (t6A) derivatives adjacent to and 3′ of the anticodons from all organisms. InEscherichia coli there are 12 such tRNA species of which two (tRNAGGU Thr1 and tRNAGGU Thr3) have the t6A derivativeN 6-methyl-N 6-threonylcarbamoyladenosine (m6t6A37). We have isolated a mutant ofE. coli that lacks the m6t6A37 in these two tRNAGGU Thr species. These tRNA species in the mutant are likely to have t6A37 instead of m6t6A37. We show that the methyl group of m6t6A37 originates fromS-adenosyl-l-methionine and that the gene (tsaA) which most likely encodes tRNA(m6t6A37)methyltransferase is located at min 4.6 on the E. coli chromosomal map. The growth rate of the cell, the polypeptide chain elongation rate, and the selection of Thr-tRNAGGU Thr to the ribosomal A site programmed with either of the cognate codons ACC and ACU were the same for thetsaA1 mutant as for the congenic wild-type strain. The expression of the threonine operon is regulated by an attenuator which contains in its leader mRNA seven ACC codons that are read by these two m6t6A37-containing tRNAGGU Thrspecies. We show that the tsaA1 mutation resulted in a twofold derepression of this operon, suggesting that the lack of the methyl group of m6t6A37 in tRNAGGU Thr slightly reduces the efficiency of this tRNA to read cognate codon ACC.

The mendelian basis of congenital heart defects

The revolution in molecular genetics is contributing to the understanding of normal and abnormal cardiovascular development and morphogenesis. Recent investigations have shown that a growing number of congenital heart malformations is due to single gene defects. The combined contribution of clinical and molecular studies is providing the chromosomal map of the genes related to these isolated cardiac defects, and to syndromes characteristically associated with specific cardiac malformations. These advances are relevant to clinical practice, since the accumulated knowledge can improve the quality of management of affected patients.