Gene expression analysis identifies hypothetical genes that may be critical during the infection process of Xanthomonas citri subsp. citri

Background: Gene expression analysis via microarray is widely used in phytobacteria to validate differential gene expression associated with virulence or to compare biological profiles of wild type and mutant strains. Here, we employed DNA microarrays to study the early stages of the infection process (24, 72 and 120 h post-inoculation) of Xanthomonas citri subsp. citri (Xac) infecting Citrus sinensis to interrogate the expression profiles of hypothetical genes. Results: Under infective conditions, 446 genes were up- and 306 downregulated. Outstanding among genes upregulated during infection were those involved in synthesizing the Type 3 Secretion System and effectors, xanthan gum and quorum-sensing induction, and flagellum synthesis and regulation. Additionally, 161 hypothetical genes were up- and 100 were downregulated, 49 of which are known to have a significant biological role. To understand hypothetical gene co-regulation or -expression, nine expression profiles including 158 genes were identified during the three infection phases. Of these, 47 hypothetical genes were identified as having expression profiles associated with at least one connected to a gene associated with adaptation and virulence. Conclusions: Expression patterns of six differentially expressed genes were validated by quantitative reverse transcription polymerase chain reaction, thus demonstrating the effectiveness of this tool in global gene expression analysis in Xac.

Can Bacillus thuringiensis affect the biological variables of natural enemies of Lepidoptera? / Bacillus thuringiensis pode afetar as variáveis biológicas de inimigos naturais de Lepidoptera?

The entomopathogen Bacillus thuringiensis (Bt) is widely used as one of the ingredients in pest control formulations, but researches conducted on its effect on non-target organisms are still in the nascent stage. This investigation aimed to uncover if Bt treated with Tenebrio molitor (Coleoptera: Tenebrionidae) larvae and pupae could affect the biological variables of Podisus nigrispinus (Hemiptera: Pentatomidae) and Palmistichus elaeisis (Hymenoptera: Eulophidae), all of which established natural enemies of leaf defoliator caterpillars in the eucalyptus culture. Larvae of T. molitor were fed on wheat bran containing different concentrations of B. thuringiensis (0.00; 0.25; 0.50; 1.00; 2.00 and 4.00 g Agree/kg bran). When the larvae attained size of about 2 cm, they were used as prey for P. nigrispinus (Bioassay I), and their pupae used as hosts for P. elaeisis (Bioassay II). Only the biological variables oviposition period and egg numbers by posture of the predator P. nigrispinus were altered. The biological variables of P. elaeisis were not altered, since it was possible to use these control methods within the integrated pest management.(AU)

O entomopatógeno Bacillus thuringiensis é amplamente empregado no controle de pragas, porém estudos de seu efeito sobre organismos não alvo ainda são incipientes. Com isso, objetivou-se neste trabalho avaliar se larvas de Tenebrio molitor (Coleoptera: Tenebrionidae), tratadas com Bacillus thuringiensis, podem afetar as variáveis biológicas de Podisus nigrispinus (Hemiptera: Pentatomidae) e Palmistichus elaeisis (Hymenoptera: Eulophidae), importantes inimigos naturais de lagartas desfolhadoras na cultura do eucalipto. Larvas de T. molitor foram alimentadas com farelo de trigo contendo diferentes concentrações de Bacillus thuringiensis (0,00; 0,25; 0,50; 1,00; 2,00 e 4,00 g de Agree®/kg farelo). Quando as larvas atingiram em média 2 cm de comprimento, foram usadas como presa para P. nigrispinus (bioensaio I) e as pupas como hospedeiro para P. elaeisis (bioensaio II). As variáveis biológicas período de oviposição e número de ovos por postura do predador P. nigrispinus foram alteradas. Já as variáveis biológicas de P. elaeisis não foram modificadas, sendo possível o uso conjunto desses métodos de controle no manejo integrado de pragas.(AU)