High levels of expression of full-length cryIA(c) gene from Bacillus thuringiensis in transgenic somatic walnut embryos

A full-length synthetic version of the cryIA(c) gene, expressing a Bacillus thuringiensis (Bt) insecticidal crystal protein (ICP), was transferred into walnut somatic embryos. Sixty one transgenic embryo lines or clones were obtained and bioassayed with first instar codling moth larvae. In 34%, of these lines, designated as 'class A', expression was high enough to obtain 80-100% mortality. A total of 20% were designated 'class B', which produced a mortality between 25 and 70% and also caused a decreased rate of larval development. Insect mortality and development from the remaining 46% of the lines were indistinguishable from that of the control. Expression of a chimeric gene encoding beta-glucuronidase (GUS) was evaluated to serve as a linked but unselected marker gene. About 62% of the class A embryo lines showed correspondingly high activity for the GUS gene. However, 38% of the class A would have been missed if the level of GUS activity was used as the sole indicator, Detectable levels of protein corresponding to cryIA(c) could be found only in class A, but not in class B or C clones. Southern analysis of border regions revealed single inserts for class A clones and multiple inserts for classes B and C. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.