Bt toxins derived from the arthropod bacterial pathogen Bacillus thuringiensis are widely used for insect control as insecticides or in transgenic crops. Bt resistance has been found in field populations of several lepidopteran pests and in laboratory strains selected with Bt toxin. Widespread planting of crops expressing Bt toxins has raised concerns about the potential increase of resistance mutations in targeted insects. By using Bombyx mori as a model, we identified a candidate gene for a recessive form of resistance to Cry1Ab toxin on chromosome 15 by positional cloning. BGIBMGA007792-93 , which encodes an ATP-binding cassette transporter similar to human multidrug resistance protein 4 and orthologous to genes associated with recessive resistance to Cry1Ac in Heliothis virescens and two other lepidopteran species, was expressed in the midgut. Sequences of 10 susceptible and seven resistant silkworm strains revealed a common tyrosine insertion in an outer loop of the predicted transmembrane structure of resistant alleles. We confirmed the role of this ATP-binding cassette transporter gene in Bt resistance by converting a resistant silkworm strain into a susceptible one by using germline transformation. This study represents a direct demonstration of Bt resistance gene function in insects with the use of transgenesis.

The root system architecture (RSA) of crops can affect their production, particularly in abiotic stress conditions, such as with drought, waterlogging, and salinity. Salinity is a growing problem worldwide that negatively impacts on crop productivity, and it is believed that yields could be improved if RSAs that enabled plants to avoid saline conditions were identified. Here, we have demonstrated, through the cloning and characterization of qSOR1 (quantitative trait locus for SOIL SURFACE ROOTING 1), that a shallower root growth angle (RGA) could enhance rice yields in saline paddies. qSOR1 is negatively regulated by auxin, predominantly expressed in root columella cells, and involved in the gravitropic responses of roots. qSOR1 was found to be a homolog of DRO1 (DEEPER ROOTING 1), which is known to control RGA. CRISPR-Cas9 assays revealed that other DRO1 homologs were also involved in RGA. Introgression lines with combinations of gain-of-function and loss-of-function alleles in qSOR1 and DRO1 demonstrated four different RSAs (ultra-shallow, shallow, intermediate, and deep rooting), suggesting that natural alleles of the DRO1 homologs could be utilized to control RSA variations in rice. In saline paddies, near-isogenic lines carrying the qSOR1 loss-of-function allele had soil-surface roots (SOR) that enabled rice to avoid the reducing stresses of saline soils, resulting in increased yields compared to the parental cultivars without SOR. Our findings suggest that DRO1 homologs are valuable targets for RSA breeding and could lead to improved rice production in environments characterized by abiotic stress.

Cardinium bacteria, members of the phylum Cytophaga-Flavobacterium-Bacteroides (CFB), are intracellular bacteria in arthropods that are capable of inducing reproductive abnormalities in their hosts, which include parasitic wasps, mites, and spiders. A high frequency of Cardinium infection was detected in planthoppers (27 out of 57 species were infected). A high frequency of Cardinium infection was also found in spider mites (9 out of 22 species were infected). Frequencies of double infection by Cardinium and Wolbachia bacteria (Alphaproteobacteria capable of manipulating reproduction of their hosts) were disproportionately high in planthoppers but not in spider mites. A new group of bacteria, phylogenetically closely related to but distinct from previously described Cardinium bacteria (based on 16S rRNA and gyrB genes) was found in 4 out of 25 species of Culicoides biting midges. These bacteria possessed a microfilament-like structure that is a morphological feature previously found in Cardinium and Paenicardinium. The bacteria close to the genus Cardinium consist of at least three groups, A, B, and C. Group A is present in various species of arthropods and was previously referred to as "Candidatus Cardinium hertigii," group B is present in plant parasitic nematodes and was previously referred to as "Candidatus Paenicardinium endonii," and group C is present in Culicoides biting midges. On the basis of morphological and molecular data, we propose that the nomenclature of these three groups be integrated into a single species, "Candidatus Cardinium hertigii."Compared to the Wolbachia bacteria, which belong to the alpha subdivision of the phylum Proteobacteria and are known as master manipulators of arthropod reproduction (48), the Cardinium bacteria, which belong to the phylum CytophagaFlavobacterium-Bacteroides (CFB), are relatively new to biological study. The phylum CFB includes many other bacteria associated with arthropods, such as symbionts in cockroaches (3) and termites (4) and the male-killing agents of ladybird beetles (21). Cardinium was first observed in tick cell cultures as an unknown intracellular prokaryote that was rod shaped and had an array of tubes extending from the cytoplasmic membrane (22). In 2001, related symbiotic bacteria were reported as manipulators of arthropod reproduction because they caused feminization, by which genetic males were converted into phenotypic females, in the false spider mite Brevipalpas obovatus (45) and parthenogenesis, in which haploid eggs were converted into viable diploid females, in the parasitoid wasp Encarsia pergandiella (50). Since the 16S rRNA gene sequences of these bacteria exhibited 96% to 98% similarity to the tick microorganism, they were classified in the phylum CFB. Subsequently, bacteria in this group were found to induce cytoplasmic incompatibility (CI), in which uninfected female hosts produce few offspring when mated with infected males in parasitic wasps of the genus Encarsia (20) and in two spider mites, Eotetranychus suginamensis and Bryobi...

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