Sequence and analysis of chromosome 4 of the plant Arabidopsis thaliana

The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.     

XANES analysis of tribochemical and thermal films generating from some organic polysulfides

X-ray absorption near edge structure (XANES) spectroscopy has been firstly used to characterize the chemical nature of tribochemical and thermal films generated from alkyl, benzyl and acyl-containing organic polysulfides. It has been found that the thermal films generated from these polysulfides are mainly composed of FeSO4, and alkyl disulfides also exist in the subsurface and bulk of thermal films generated from acyl-containing polysulfides. Under tribochemical conditions, the composition of film is dependent on the molecular structure of the additives. Namely, the tribochemical film generated from alkyl polysulfide is composed of alkyl disulfide in the out surface, a mixture of FeSO4, FeS2 and sulfoxide in the subsurface, and FeSO4 in the bulk; the composition of the tribochemical film for benzyl polysulfide consists of FeSO4 in the out surface, while the composition in subsurface and bulk is the same as the alkyl polysulfide. For acyl-containing polysulfides, the tribochemical films consist of alkyl disulfide in the out surface, and FeS2 in the subsurface and bulk.     

The genome of the mesopolyploid crop species Brassica rapa

We report the annotation and analysis of the draft genome sequence of Brassica rapa accession Chiifu-401-42, a Chinese cabbage. We modeled 41,174 protein coding genes in the B. rapa genome, which has undergone genome triplication. We used Arabidopsis thaliana as an outgroup for investigating the consequences of genome triplication, such as structural and functional evolution. The extent of gene loss (fractionation) among triplicated genome segments varies, with one of the three copies consistently retaining a disproportionately large fraction of the genes expected to have been present in its ancestor. Variation in the number of members of gene families present in the genome may contribute to the remarkable morphological plasticity of Brassica species. The B. rapa genome sequence provides an important resource for studying the evolution of polyploid genomes and underpins the genetic improvement of Brassica oil and vegetable crops.