Multiple invasions of Gypsy and Micropia retroelements in genus Zaprionus and melanogaster subgroup of the genus Drosophila

<p>Abstract</p> <p>Background</p> <p>The <it>Zaprionus </it>genus shares evolutionary features with the <it>melanogaster </it>subgroup, such as space and time of origin. Although little information about the transposable element content in the <it>Zaprionus </it>genus had been accumulated, some of their elements appear to be more closely related with those of the <it>melanogaster </it>subgroup, indicating that these two groups of species were involved in horizontal transfer events during their evolution. Among these elements, the <it>Gypsy </it>and the <it>Micropia </it>retroelements were chosen for screening in seven species of the two <it>Zaprionus </it>subgenera, <it>Anaprionus </it>and <it>Zaprionus</it>.</p> <p>Results</p> <p>Screening allowed the identification of diverse <it>Gypsy </it>and <it>Micropia </it>retroelements only in species of the <it>Zaprionus </it>subgenus, showing that they are transcriptionally active in the sampled species. The sequences of each retroelement were closely related to those of the <it>melanogaster </it>species subgroup, and the most parsimonious hypothesis would be that 15 horizontal transfer events shaped their evolution. The <it>Gypsy </it>retroelement of the <it>melanogaster </it>subgroup probably invaded the <it>Zaprionus </it>genomes about 11 MYA. In contrast, the <it>Micropia </it>retroelement may have been introduced into the <it>Zaprionus </it>subgenus and the <it>melanogaster </it>subgroup from an unknown donor more recently (~3 MYA).</p> <p>Conclusion</p> <p><it>Gypsy </it>and <it>Micropia </it>of <it>Zaprionus </it>and <it>melanogaster </it>species share similar evolutionary patterns. The sharing of evolutionary, ecological and ethological features probably allowed these species to pass through a permissive period of transposable element invasion, explaining the proposed waves of horizontal transfers.</p

Characterization of new IS elements and studies of their dispersion in two subspecies of Leifsonia xyli

<p>Abstract</p> <p>Background</p> <p><it>Leifsonia xyli </it>is a xylem-inhabiting bacterial species comprised of two subspecies: <it>L. xyli </it>subsp. <it>xyli </it>(<it>Lxx</it>) and <it>L. xyli </it>subsp. <it>cynodontis </it>(<it>Lxc</it>). <it>Lxx </it>is the causal agent of ratoon stunting disease in sugarcane commercial fields and <it>Lxc </it>colonizes the xylem of several grasses causing either mild or no symptoms of disease. The completely sequenced genome of <it>Lxx </it>provided insights into its biology and pathogenicity. Since IS elements are largely reported as an important source of bacterial genome diversification and nothing is known about their role in chromosome architecture of <it>L. xyli</it>, a comparative analysis of <it>Lxc </it>and <it>Lxx </it>elements was performed.</p> <p>Results</p> <p>Sample sequencing of <it>Lxc </it>genome and comparative analysis with <it>Lxx </it>complete DNA sequence revealed a variable number of IS transposable elements acting upon genomic diversity. A detailed characterization of <it>Lxc </it>IS elements and a comparative review with IS elements of <it>Lxx </it>are presented. Each genome showed a unique set of elements although related to same IS families when considering features such as similarity among transposases, inverted and direct repeats, and element size. Most of the <it>Lxc </it>and <it>Lxx </it>IS families assigned were reported to maintain transposition at low levels using translation regulatory mechanisms, consistent with our <it>in silico </it>analysis. Some of the IS elements were found associated with rearrangements and specific regions of each genome. Differences were also found in the effect of IS elements upon insertion, although none of the elements were preferentially associated with gene disruption. A survey of transposases among genomes of Actinobacteria showed no correlation between phylogenetic relatedness and distribution of IS families. By using Southern hybridization, we suggested that diversification of <it>Lxc </it>isolates is also mediated by insertion sequences in probably recent events.</p> <p>Conclusion</p> <p>Collectively our data indicate that transposable elements are involved in genome diversification of <it>Lxc </it>and <it>Lxx</it>. The IS elements were probably acquired after the divergence of the two subspecies and are associated with genome organization and gene contents. In addition to enhancing understanding of IS element dynamics in general, these data will contribute to our ongoing comparative analyses aimed at understanding the biological differences of the <it>Lxc </it>and <it>Lxx</it>.</p

An operon for production of bioactive gibberellin A4 phytohormone with wide distribution in the bacterial rice leaf streak pathogen Xanthomonas oryzae pv. oryzicola

• Phytopathogens have developed elaborate mechanisms to attenuate the defense response of their host plants, including convergent evolution of complex pathways for production of the gibberellin (GA) phytohormones, which were actually first isolated from the rice fungal pathogen Gibberella fujikuroi. The rice bacterial pathogen Xanthomonas oryzae pv. oryzicola (Xoc) has been demonstrated to contain a biosynthetic operon with cyclases capable of producing the universal GA precursor ent-kaurene. Genetic (knock-out) studies indicate that the derived diterpenoid serves as a virulence factor for this rice leaf streak pathogen, serving to reduce the jasmonic acid (JA) mediated defense response. • Here the function of the remaining genes in the Xoc operon are elucidated and the distribution of the operon in X. oryzae investigated in over 100 isolates. • The Xoc operon leads to production of the bioactive GA4, an additional step beyond production of the penultimate precursor GA9 mediated by the homologous operons recently characterized from rhizobia. Moreover, this GA biosynthetic operon was found to be widespread in Xoc (\u3e90%), but absent in the other major oryzae pathovar. • These results indicate selective pressure for production of GA4 in the distinct lifestyle of Xoc, and the importance of GA to both fungal and bacterial pathogens of rice