RESUMO
Citrus tristeza virus (CTV) is the major virus pathogen causing significant economic damage to citrus worldwide, and a single dominant gene, Ctv, provides broad spectrum resistance to CTV in Poncirus trifoliata L. Raf. Ctv was physically mapped to a 282-kb region using a P. trifoliata bacterial artificial chromosome library. This region was completely sequenced to about 8x coverage using a shotgun sequencing strategy and primer walking for gap closure. Sequence analysis predicts 22 putative genes, two mutator-like transposons and eight retrotransposons. This sequence analysis also revealed some interesting features of this region of the P. trifoliata genome: a disease resistance gene cluster with seven members and eight retrotransposons clustered in a 125-kb gene-poor region. Comparative sequence analysis suggests that six genes in the Ctv region have significant sequence similarity with their orthologs in bacterial artificial chromosome clones F7H2 and F21T11 from Arabidopsis chromosome I. However, the analysis of gene colinearity between P. trifoliata and Arabidopsis indicates that Arabidopsis genome sequence information may be of limited use for positional gene cloning in P. trifoliata and citrus. Analysis of candidate genes for Ctv is also discussed.
Assuntos
Doenças das Plantas/genética , Proteínas de Plantas/genética , Vírus de Plantas/crescimento & desenvolvimento , Poncirus/genética , Sequência de Aminoácidos , Arabidopsis/genética , Cromossomos Artificiais Bacterianos/genética , Clonagem Molecular , Mapeamento de Sequências Contíguas , Elementos de DNA Transponíveis/genética , DNA de Plantas/química , DNA de Plantas/genética , Genoma de Planta , Imunidade Inata/genética , Dados de Sequência Molecular , Família Multigênica , Filogenia , Doenças das Plantas/virologia , Poncirus/virologia , Sequências Repetitivas de Ácido Nucleico/genética , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , SinteniaRESUMO
The variations of concentrations of hexachloro-cyclohexane (HCHs), dichloro diphenyl trichloroethane (DDTs) in surface sediments from the Changjiang Estuary and Zhejiang coastal area suggests that although there is a substantial decrease of these persistent trace compounds since the last two decades, they still presented in recent surface sediments. Their concentration levels in suspended matter are still quite high. In dated sedimentary cores, the DDTs and HCHs concentration peaks appeared in 1960s to 1980s, which approximately corresponded to their production and usage history.