The genome sequence of the plant pathogen Xylella fastidiosa. The Xylella fastidiosa Consortium of the Organization for Nucleotide Sequencing and Analysis

Xylella fastidiosa is a fastidious, xylem-limited bacterium that causes a range of economically important plant diseases. Here we report the complete genome sequence of X. fastidiosa clone 9a5c, which causes citrus variegated chlorosis--a serious disease of orange trees. The genome comprises a 52.7% GC-rich 2,679,305-base-pair (bp) circular chromosome and two plasmids of 51,158 bp and 1,285 bp. We can assign putative functions to 47% of the 2,904 predicted coding regions. Efficient metabolic functions are predicted, with sugars as the principal energy and carbon source, supporting existence in the nutrient-poor xylem sap. The mechanisms associated with pathogenicity and virulence involve toxins, antibiotics and ion sequestration systems, as well as bacterium-bacterium and bacterium-host interactions mediated by a range of proteins. Orthologues of some of these proteins have only been identified in animal and human pathogens; their presence in X. fastidiosa indicates that the molecular basis for bacterial pathogenicity is both conserved and independent of host. At least 83 genes are bacteriophage-derived and include virulence-associated genes from other bacteria, providing direct evidence of phage-mediated horizontal gene transfer.     

A mirror-symmetric cell division that orchestrates neuroepithelial morphogenesis

The development of cell polarity is an essential prerequisite for tissue morphogenesis during embryogenesis, particularly in the development of epithelia. In addition, oriented cell division can have a powerful influence on tissue morphogenesis. Here we identify a novel mode of polarized cell division that generates pairs of neural progenitors with mirror-symmetric polarity in the developing zebrafish neural tube and has dramatic consequences for the organization of embryonic tissue. We show that during neural rod formation the polarity protein Pard3 is localized to the cleavage furrow of dividing progenitors, and then mirror-symmetrically inherited by the two daughter cells. This allows the daughter cells to integrate into opposite sides of the developing neural tube. Furthermore, these mirror-symmetric divisions have powerful morphogenetic influence: when forced to occur in ectopic locations during neurulation, they orchestrate the development of mirror-image pattern formation and the consequent generation of ectopic neural tubes.     

DNA polymerases in human platelets]

Human platelets have two DNA polymerases. In the mitochondrial-free cytoplasm we have found a DNA polymerase gamma and another DNA polymerase very closely related to the polymerase alpha from animal cells. In the mitochondria only the gamma activity is present.     

Current status of the non-indigenous molluscs in Chile,with the first record of Otala punctata (Müller, 1774) (Gastropoda: Helicidae) in the country and new records for Cornu aspersum (Müller, 1774) and Deroceras laeve (Müller, 1774)

A new introduced species, Otala punctata (Müller, 1774) and new records in Chile for Cornu aspersum (Müller, 1774) and Deroceras laeve (Müller, 1774) are documented based on surveys carried out in northern and central areas of the country. The presence and distribution of these alien species are complemented with a comprehensive compilation of all 34 non-indigenous species of marine, freshwater and terrestrial Mollusca in Chile; until 1999, only 16 alien species were known in Chile. Most of these alien species are found exclusively in transformed habitats, few exist in natural environments. The mechanism of introduction for the majority of these non-indigenous species is unknown; however, horticultural development, urban and suburban transformation of original natural habitats, and the aquarium trade are the most likely pathways of introduction. The highest threat of alien species is direct competition and predation of native molluscs, especially the small native land gastropods. Education and continuous field surveys are vital to detect and prevent their propagation as well as to avoid introduction of additional alien taxa.