A New approach to the practical use of insect-tolerant lines of sugar beet via foreign gene transfer

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The larvae of cabbage armyworm (Mamestra brassicae L.) bring heavy damage on the final yield of beet-roots and subsequently, sugar production, by eating stems and leaves of sugar beet plants. In order to establish sugar beet cultivars that are tolerant to insects including cabbage armyworm, we have been developing transgenic sugar beet lines harboring cryIA(b), a gene encoding insecticide protein from Bacillus thuringiensis. In the present study, based on the results so far obtained, we tried to make transgenic sugar beet lines that show increased insecticide activity aiming at practical use of the transgenic lines. First, we introduced cryIC into sugar beet plants and analyzed the effect of its expression. We chose cryIC from various candidates of insecticide protein genes, since its gene product showed highest insecticide activity against cabbage armyworm among various insecticide proteins that were obtained by expressing cloned genes in E. coli. Meanwhile, reports were published that described that the introduction of insecticide protein genes into chloroplast gave increased accumulation of the protein and consequently, gave increased insecticide activity of plants. We, therefore, developed vectors available for chloroplast transformation and selection system of transformed chloroplast in order to introduce insecticide protein genes into sugar beet chloroplasts. We also succeeded in introducing several genes practically useful for sugar beet production and evaluated the effect of gene expression. In addition, we analyzed the stability of the expression of foreign genes in plant cells in order to make sure their experssion.