The development of resistance is the main threat to the long-term use of toxins from Bacillus thuringiensis (Bt) in transgenic plants. Here we report the cloning of a Bt toxin resistance gene, Caenorhabditis elegans bre-5, which encodes a putative beta-1,3-galactosyltransferase. Lack of bre-5 in the intestine led to resistance to the Bt toxin Cry5B. Wild-type but not bre-5 mutant animals were found to uptake toxin into their gut cells, consistent with bre-5 mutants lacking toxin-binding sites on their apical gut. bre-5 mutants displayed resistance to Cry14A, a Bt toxin lethal to both nematodes and insects; this indicates that resistance by loss of carbohydrate modification is relevant to multiple Bt toxins.

Crystal (Cry) proteins made by the bacterium Bacillus thuringiensis are pore-forming toxins that specifically target insects and nematodes and are used around the world to kill insect pests. To better understand how pore-forming toxins interact with their host, we have screened for Caenorhabditis elegans mutants that resist Cry protein intoxication. We find that Cry toxin resistance involves the loss of two glycosyltransferase genes, bre-2 and bre-4. These glycosyltransferases function in the intestine to confer susceptibility to toxin. Furthermore, they are required for the interaction of active toxin with intestinal cells, suggesting they make an oligosaccharide receptor for toxin. Similarly, the bre-3 resistance gene is also required for toxin interaction with intestinal cells. Cloning of the bre-3 gene indicates it is the C. elegans homologue of the Drosophila egghead (egh) gene. This identification is striking given that the previously identified bre-5 has homology to Drosophila brainiac (brn) and that egh-brn likely function as consecutive glycosyltransferases in Drosophila epithelial cells. We find that, like in Drosophila, bre-3 and bre-5 act in a single pathway in C. elegans. bre-2 and bre-4 are also part of this pathway, thereby extending it. Consistent with its homology to brn, we demonstrate that C. elegans bre-5 rescues the Drosophila brn mutant and that BRE-5 encodes the dominant UDP-GlcNAc:Man GlcNAc transferase activity in C. elegans. Resistance to Cry toxins has uncovered a four component glycosylation pathway that is functionally conserved between nematodes and insects and that provides the basis of the dominant mechanism of resistance in C. elegans.

BackgroundPatients with Hb E/β0 thalassemia display remarkable variability in disease severity. To identify genetic modifiers influencing disease severity, we conducted a two-stage genome scan in groups of 207 mild and 305 severe unrelated patients from Thailand with Hb E/β0 thalassemia and normal α-globin genes.MethodsFirst, we estimated and compared the allele frequencies of approximately 110,000 gene-based single nucleotide polymorphisms (SNPs) in pooled DNAs from different severity groups. The 756 SNPs that showed reproducible allelic differences at P < 0.02 by pooling were selected for individual genotyping.ResultsAfter adjustment for age, gender and geographic region, logistic regression models showed 50 SNPs significantly associated with disease severity (P < 0.05) after Bonferroni adjustment for multiple testing. Forty-one SNPs in a large LD block within the β-globin gene cluster had major alleles associated with severe disease. The most significant was bthal_bg200 (odds ratio (OR) = 5.56, P = 2.6 × 10-13). Seven SNPs in two distinct LD blocks within a region centromeric to the β-globin gene cluster that contains many olfactory receptor genes were also associated with disease severity; rs3886223 had the strongest association (OR = 3.03, P = 3.7 × 10-11). Several previously unreported SNPs were also significantly associated with disease severity.ConclusionsThese results suggest that there may be an additional regulatory region centromeric to the β-globin gene cluster that affects disease severity by modulating fetal hemoglobin expression.

We evaluated the contribution of 67 single nucleotide polymorphisms (SNPs) within the beta-globin gene cluster to disease severity in groups of 207 mild- and 305 severe unrelated patients from Thailand with Hemoglobin E (HbE)/beta(0)-thalassemia and normal alpha-globin genes. Our analysis showed that these SNPs comprise two distinct linkage disequilibrium blocks, one containing the beta-globin gene and the other extending from the locus control region (LCR) to the delta gene, which are separated by a recombination hotspot in the narrow region of the beta-globin gene promoter. Forty-five SNPs within the interval including the LCR region and the delta gene showed strong association with disease severity. The strongest association was observed with the XmnI polymorphism located 158-bp upstream to the G gamma gene (p = 4.6E-12). Carriers of the T allele of XmnI were more likely to have a milder disease course and higher level of fetal hemoglobin (HbF) in both the mild (p = 0.005) and severe (p = 8.7E-06) patient groups. Haplotype analysis revealed that the T allele of XmnI was nearly always in cis with the HbE allele. The high frequency of this haplotype may be favored by positive selection against malarial infection. Further studies are needed to validate this hypothesis and determine whether XmnI or another closely linked variant modulates severity and HbF levels in patients with beta(0)-thalassemia/HbE disease.