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Interactions of Insecticidal Toxin Gene Products from Xenorhabdus nematophilus PMFI296

Interactions of Insecticidal Toxin Gene Products from Xenorhabdus nematophilus PMFI296,10.1128/AEM.69.6.3344-3349.2003,Applied and Environmental Micro

Interactions of Insecticidal Toxin Gene Products from Xenorhabdus nematophilus PMFI296   (Citations: 33)
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Four genes on a genomic fragment from Xenorhabdus nematophilus PMFI296 were shown to be involved in insecticidal activity towards three commercially important insect species. Each gene was expressed individually and in combinations in Escherichia coli, and the insecticidal activity of the lysates was determined. The combined four genes (xptA1, xptA2, xptB1, and xptC1), in E. coli, showed activity towards Pieris brassicae, Pieris rapae, and Heliothis virescens. The genes xptA1, xptB1, and xptC1 were involved in expressing activity towards P. rapae and P. brassicae, while the genes xptA2, xptB1, and xptC1 were needed for activity towards H. virescens. When each of these three genes was expressed individually in E. coli and the cell lysates were used in insect assays or mixed and then used, insecticidal activity was detected at a very low level. If the genes xptB1 and xptC1 were expressed in the same E. coli cell and this cell lysate was mixed with cells expressing xptA1, activity was restored to P. rapae and P. brassicae. Similarly mixing XptB1/C1 lysate with XptA2 lysate restored activity towards H. virescens. Individual gene disruptions in X. nematophilus PMFI296 reduced activity to insects; this activity was restored by complementation with cells expressing either xptA1 or xptA2 for their respective disruptions or E. coli expressing both xptB1 and xptC1 for individual disruptions of either of these genes. The genes xptA2, xptC1, and xptB1 were expressed as an operon in PMFI296 and inactivation of xptA2 or xptC1 resulted in silencing of downstream gene(s), while xptA1 was expressed as a single gene. Therefore, the two three gene product combinations interact with each other to produce good insecticidal activity. New insecticidal toxins with activity towards pests of com- mercial importance are needed for either the development of sprayable products or transgenic plants. We have previously described a group of toxins from Xenorhabdus species that kill lepidopteran insects. The genes responsible for this insecticidal activity were identified by screening a cosmid genomic library, expressed in Escherichia coli. One cosmid (CHRIM1) con- tained five genes related to insecticidal activity (12). One of these genes (xptA1) was central for insecticidal activity towards Pieris brassicae, and when expressed in E. coli, a low level of insecticidal activity was observed. However for full insecticidal activity a much larger region of DNA comprising xptA1 and at least two other genes, xptB1 and xptC1, was required. The precise genetic nature of toxin combinations resulting in insec- ticidal activity and their effect upon other insects had not been determined. Genes homologous to those present on CHRIM1 have also been described in Photorhabdus luminescens (1, 10), a symbiont of entomopathogenic nematodes closely related to Xenorhab- dus species. The requirement of three genes equivalent to xptA1, xptB1, and xptC1 in the expression of full insecticidal activity towards the model insect Manduca sexta (tobacco horn- worm) was shown first in P. luminescens strain Hb (10) and later in P. luminescens strain W14 (13). Homologous genes to xptA1, xptB1, and xptC1 have also been identified in Serratia entomophila (7), where some species are the causative agent of
Journal: Applied and Environmental Microbiology - AEM , vol. 69, no. 6, pp. 3344-3349, 2003
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