Rare and fleeting: an example of interspecific recombination in animal mitochondrial DNA

Recombination is thought to occur only rarely in animal mitochondrial DNA ( mtDNA). However, detection of mtDNA recombination requires that cells become heteroplasmic through mutation, intramolecular recombination or ' leakage' of paternal mtDNA. Interspecific hybridization increases the probability of detecting mtDNA recombinants due to higher levels of sequence divergence and potentially higher levels of paternal leakage. During a study of historical variation in Atlantic salmon ( Salmo salar) mtDNA, an individual with a recombinant haplotype containing sequence from both Atlantic salmon and brown trout ( Salmo trutta) was detected. The individual was not an F1 hybrid but it did have an unusual nuclear genotype which suggested that it was a later-generation backcross. No other similar recombinant haplotype was found from the same population or three neighbouring Atlantic salmon populations in 717 individuals collected during 1948 - 2002. Interspecific recombination may increase mtDNA variability within species and can have implications for phylogenetic studies

Distribution of hepatitis B virus genotypes and viral load levels in Brazilian chronically infected patients in São Paulo city Distribuição dos genótipos do vírus da hepatite B e níveis de carga viral em pacientes brasileiros cronicamente infectados na cidade de São Paulo

The objective of the present study was to evaluate the serum viral load in chronically infected Hepatitis B virus (HBV) patients and to investigate the distribution of HBV genotypes in São Paulo city. Quantitative HBV-DNA assays and HBV genotyping have gained importance for predicting HBV disease progression, have been employed for assessing infectivity, for treatment monitoring and for detecting the emergence of drug resistance. Twenty-nine Brazilian patients with suspected chronic hepatitis B were studied, using real time PCR for viral load determination and direct DNA sequencing for the genotyping. The serology revealed chronic HBV infection in 22 samples. The HBV-DNA was positive in 68% samples (15/22). The phylogenetic analysis disclosed that eleven patients were infected with HBV genotype A, two with genotype F and two with genotype D. Thus, the genotype A was the most prevalent in our study.<br>O objetivo do presente estudo foi avaliar a carga viral no soro de pacientes cronicamente infectados pelo vírus da Hepatite B (HBV) e investigar a distribuição de genótipos HBV na cidade de São Paulo. PCR quantitativo do HBV e genotipagem ganharam importância para a previsão de progressão da doença, empregada para avaliar a infectividade, para tratamento e acompanhamento e para detectar o aparecimento de resistência aos anti-retrovirais. Vinte e nove pacientes brasileiros com suspeita de hepatite B crônica foram estudados, utilizando PCR em tempo real para a determinação da carga viral e seqüenciamento direto para determinação do genótipo. A sorologia revelou que 22 estavam, de fato, cronicamente infectados pelo HBV. O HBV-DNA foi positivo em 68% das amostras (15/22). Em sete casos, HBV-DNA foi indetectável por PCR quantitativo. A análise filogenética mostra que onze pacientes foram infectados com hepatite B genótipo A, dois com genótipo F e dois com genótipo D. Desta forma, o genótipo A foi o mais prevalente em nosso estudo

Stem pitting and seedling yellows symptoms of Citrus tristeza virus infection may be determined by minor sequence variants

The isolates of Citrus tristeza virus (CTV), the most destructive viral pathogen of citrus, display a high level of variability. As a result of genetic bottleneck induced by the bud-inoculation of CTV-infected material, inoculated seedlings of Citrus wilsonii Tanaka displayed different symptoms. All successfully grafted plants showed severe symptoms of stem pitting and seedling yellows, while plants in which inoculated buds died displayed mild symptoms. Since complex CTV population structure was detected in the parental host, the aim of this work was to investigate how it changed after the virus transmission, and to correlate it with observed symptoms. The coat protein gene sequence of the predominant genotype was identical in parental and grafted plants and clustered to the phylogenetic group 5 encompassing severe reference isolates. In seedlings displaying severe symptoms, the low-frequency variants clustering to other phylogenetic groups were detected, as well. Indicator plants were inoculated with buds taken from unsuccessfully grafted C. wilsonii seedlings. Surprisingly, they displayed no severe symptoms despite the presence of phylogenetic group 5 genomic variants. The results suggest that the appearance of severe symptoms in this case is probably induced by a complex CTV population structure found in seedlings displaying severe symptoms, and not directly by the predominant genomic variant