Bacillus thuringiensis is a Gram-positive aerobic bacterium that produces insecticidal crystalline inclusions during sporulation phases of the mother cell. The vir- ulence factor, known as parasporal crystals, is comp...Bacillus thuringiensis is a Gram-positive aerobic bacterium that produces insecticidal crystalline inclusions during sporulation phases of the mother cell. The vir- ulence factor, known as parasporal crystals, is composed of Cry and Cyt toxins. Most Cry toxins display a common 3-domain topology. Cry toxins exert intoxication through toxin activation, receptor binding and pore formation in a suitable larval gut environment. The mosquitocidal toxins of Bt subsp, israelensis （Bti） were found to be highly active against mosquito larvae and are widely used for vector control. Bt subsp, jegathesan is another strain which possesses high potency against broad range of mosquito larvae. The present review summarizes characterized receptors for Cry toxins in mosquito larvae, and will also discuss the diversity and effects of 3-D mosquitocidal Cry toxin and the ongo- ing research for Cry toxin mechanisms generated from investigations of lepidopteran and dipteran larvae.展开更多
Bacillus thuringiensis(Bt)toxins are effective in controlling insect pests either through the spraying of products or when expressed in transgenic crops.The discovery of endophytic Bt strains opened new perspectives f...Bacillus thuringiensis(Bt)toxins are effective in controlling insect pests either through the spraying of products or when expressed in transgenic crops.The discovery of endophytic Bt strains opened new perspectives for studies aimed at the control of sap‐sucking insects,such as the Asian citrus psyllid Diaphorina citri Kuwayama(Hemiptera:Liviidae),a vector of“Candidatus Liberibacter spp.,”associated with citrus huanglongbing(HLB).In this study,translocation of endophytic Bt strains in citrus seedlings inoculated with Bt suspension delivered by soil‐drench,and their systemic pathogenicity to D.citri nymphs were investigated.The pathogenicity of three wild‐type Bt strains against D.citri third‐instar nymphs was demonstrated.Among the 10 recombinant strains tested(each of them harboring a single cry or cyt gene),3 can be highlighted,causing 42%–77%and 66%–90%nymphal mortality at 2 and 5 d after inoculation,respectively.The isolation of Bt cells from young citrus shoots and dead nymphs,and PCR performed with specific primers,confirmed the involvement of the Bt strains in the psyllid mortality.This is the first report showing the translocation of Bt strains from citrus seedling roots to shoots and their potential to control D.citri nymphs that fed on these soil‐drench inoculated seedlings.The Bt strains that caused the highest mortality rates have the potential to be used as bioinsecticides to control D.citri and the identified genes can be used for the production of transgenic Bt citrus.展开更多
文摘Bacillus thuringiensis is a Gram-positive aerobic bacterium that produces insecticidal crystalline inclusions during sporulation phases of the mother cell. The vir- ulence factor, known as parasporal crystals, is composed of Cry and Cyt toxins. Most Cry toxins display a common 3-domain topology. Cry toxins exert intoxication through toxin activation, receptor binding and pore formation in a suitable larval gut environment. The mosquitocidal toxins of Bt subsp, israelensis （Bti） were found to be highly active against mosquito larvae and are widely used for vector control. Bt subsp, jegathesan is another strain which possesses high potency against broad range of mosquito larvae. The present review summarizes characterized receptors for Cry toxins in mosquito larvae, and will also discuss the diversity and effects of 3-D mosquitocidal Cry toxin and the ongo- ing research for Cry toxin mechanisms generated from investigations of lepidopteran and dipteran larvae.
基金This study was financed in part by the Coordenacao de Aperfeigoamento de Pessoal de Nivel Superior-Brasil(CAPES)and by the Brazilian Agricultural Research Corporation(EMBRAPA-grant number 03.13.03.006.00.00)。
文摘Bacillus thuringiensis(Bt)toxins are effective in controlling insect pests either through the spraying of products or when expressed in transgenic crops.The discovery of endophytic Bt strains opened new perspectives for studies aimed at the control of sap‐sucking insects,such as the Asian citrus psyllid Diaphorina citri Kuwayama(Hemiptera:Liviidae),a vector of“Candidatus Liberibacter spp.,”associated with citrus huanglongbing(HLB).In this study,translocation of endophytic Bt strains in citrus seedlings inoculated with Bt suspension delivered by soil‐drench,and their systemic pathogenicity to D.citri nymphs were investigated.The pathogenicity of three wild‐type Bt strains against D.citri third‐instar nymphs was demonstrated.Among the 10 recombinant strains tested(each of them harboring a single cry or cyt gene),3 can be highlighted,causing 42%–77%and 66%–90%nymphal mortality at 2 and 5 d after inoculation,respectively.The isolation of Bt cells from young citrus shoots and dead nymphs,and PCR performed with specific primers,confirmed the involvement of the Bt strains in the psyllid mortality.This is the first report showing the translocation of Bt strains from citrus seedling roots to shoots and their potential to control D.citri nymphs that fed on these soil‐drench inoculated seedlings.The Bt strains that caused the highest mortality rates have the potential to be used as bioinsecticides to control D.citri and the identified genes can be used for the production of transgenic Bt citrus.
