Bombyx mori, BT toxin, anchor locus
The BT toxin is an insecticide produced by the bacterium Bacillus thuringiensis, and millions of acres of genetically modified crops expressing this agent have been planted. However, with such widespread use, there is a great potential for pests resistant to this toxin to develop. An understanding of how BT resistance operates and is inherited is central to ensuring continued use of the transgenic crops. Bombyx mori, the domesticated silkworm, is the model organism for the Lepidoptera, an order of insects containing many important agricultural pests. Screening shows that BT resistance is present in some silkworm strains, and linkage group 15 (LG15) harbors a major BT resistance factor (W. Hara, personal communication). We have found BT resistance in a different silkworm strain, and are testing to determine if the same linkage group is responsible. To do this we chose ribosomal protein (Rp) genes, which also mapped to this chromosome, as candidates for genetic markers. Because these genes are orthologous, meaning that they are present in related species and are derived from the same ancestor, they are considered to be anchor loci, which can be applied to a variety of species. By comparing genomic and cDNA sequences of Rp genes, I identified introns, likely to be the most polymorphic areas of a gene, for amplification by polymerase chain reaction. Using a mapping panel prepared by a graduate of the Goldsmith lab, analysis with one anchor locus suggests that the resistance phenotype does indeed map to LG15. More markers that have been mapped to this chromosome are being scanned in an effort to corroborate this finding. Recent publications have shown that there is strong synteny, the conservation of chromosomal linkage of orthologous genes, within the Lepidoptera. As such, it is expected that these anchor loci will be present on the same linkage group as the putative BT resistance factor in related species, and therefore of use to future studies.