RESUMO
The fastidious bacterium Xylella fastidiosa is associated with important crop diseases worldwide. We have recently shown that X. fastidiosa is a peculiar organism having unusually low values of gene codon bias throughout its genome and, unexpectedly, in the group of the most abundant proteins. Here, we hypothesized that the lack of codon usage optimization in X. fastidiosa would incapacitate this organism to undergo quick and massive changes in protein expression as occurs in a classical stress response. Proteomic analysis of the response to heat stress in X. fastidiosa revealed that no changes in protein expression can be detected. Moreover, stress-inducible proteins identified in the closely related citrus pathogen Xanthomonas axonopodis pv citri were found to be constitutively expressed in X. fastidiosa. These proteins have extremely high codon bias values in the X. citri and other well-studied organisms, but low values in X. fastidiosa. Because biased codon usage is well known to correlate to the rate of protein synthesis, we speculate that the peculiar codon bias distribution in X. fastidiosa is related to the absence of a classical stress response, and, probably, alternative strategies for survival of X. fastidiosa under stressfull conditions.
Assuntos
Citrus/microbiologia , Resposta ao Choque Térmico , Xylella/fisiologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Chaperonina 10/genética , Chaperonina 10/metabolismo , Regulação Bacteriana da Expressão Gênica , Proteínas de Choque Térmico/genética , Proteínas de Choque Térmico/metabolismo , Doenças das Plantas/microbiologia , Xanthomonas/patogenicidade , Xanthomonas/fisiologia , Xylella/genética , Xylella/metabolismo , Xylella/patogenicidadeRESUMO
Nearly 65,000 citrus EST (Expressed Sequence Tags) have been investigated using the CitEST project database. Microsatellites were investigated in the unigene sequences from Citrus spp. and Poncirus trifoliata. From these sequences, approximately 35 percent of the non-redundant ESTs contained SSRs. The frequencies of different SSR motifs were similar between Citrus spp and trifoliate orange. In general, mononucleotide repeats appeared to be the most abundant SSRs in the CitEST database, but we also identify di-, tri-, tetra-, penta- and hexanucleotide repeats. The AG/CT and AAG/CTT were the most common dinucleotide and trinucleotide motifs, with frequencies of 54.4 percent and 25.2 percent, respectively. Primer sequences flanking SSR motifs were successfully designed and synthesized. After in silico polymorphism analysis, a subset of sixty-eight primers was validated in different Citrus spp. and Poncirus trifoliata. PCR-amplification revealed polymorphism in citrus with all tested primer pairs and showed the potential of these markers for linkage mapping. Our study showed that the CitEST database can be exploited for the development of SSR markers that can amplify Citrus spp. and related genus for comparative mapping and other genetic analyses.
RESUMO
DNA macroarrays of 279 genes of Xanthomonas axonopodis pv. citri potentially associated with pathogenicity and virulence were used to compare the transcriptional alterations of this bacterium in response to two synthetic media. Data analysis indicated that 31 genes were up-regulated by synthetic medium XVM2, while only 7 genes were repressed. The results suggest that XVM2 could be used as an in vitro system to identify candidate genes involved in pathogenesis of X. axonopodis pv. citri.
Assuntos
Perfilação da Expressão Gênica , Regulação Bacteriana da Expressão Gênica/genética , Virulência/genética , Xanthomonas/genética , Xanthomonas/patogenicidade , Sequência de Bases , Sequência Conservada , Genes Bacterianos/genética , Análise de Sequência com Séries de OligonucleotídeosRESUMO
Citrus leprosis virus (CiLV), a tentative member of the Rhabdoviridae family, affects citrus trees in Brazil, where it is transmitted by mites Brevipalpus spp. It also occurs in other South American countries and was recently identified in Central America. This northbound spread of CiLV is being considered a serious threat to the citrus industry of the United States. However, despite its importance, difficulties related to the biology of CiLV have hindered much of the progress regarding its accurate detection, leaving both the analyses of symptoms and electron microscopy as the only tools available. An attempt to overcome this problem was made by constructing a cDNA library from double-stranded RNA extracted from leprosis lesions of infected Citrus sinensis (sweet orange) leaves. After cloning and sequencing, specific primers were designed to amplify putative CiLV genome regions with similarity to genes encoding the movement protein and replicase of other plant viruses. RNA from infected citrus plants corresponding to different varieties and locations were amplified by reverse transcription-polymerase chain reaction (RT-PCR) using the two pairs of primers. Amplified products were purified, cloned in pGEM-T, and sequenced. The sequences confirmed the genomic regions previously associated with CiLV. The results demonstrate that RT-PCR was specific, accurate, rapid, and reliable for the detection of CiLV.