[Studies on the distorted segregation of foreign genes in transgenic rice progenies]

The segregation mode of transgenes was investigated in the transgenic progenies of three rice varieties (lines) produced by Agrobacterium-mediated transformation. The transgenic lines all contained the Bacillus thuringiensis cry1Ab gene, under the control of a maize ubiquitin promoter, and linked in tandem with gusA and hpt genes. PCR analysis showed the transgenes cry1Ab and gusA co-segregated in all self and crossed progenies tested. Therefore, GUS bio-assay of leaf or endosperm tissues was used to monitor transgene segregation in the experiment. It was found that the ratio of positive to negative plants was significantly smaller than 3:1 in all heterozygous plants derived progenies, which implied the segregation biased from typical Mendelian mode for a single dominant gene. Less GUS positive plants, and consequently less homozygous transgenic lines than expected were recovered from the self progenies. Transgenic heterozygous plants (+/-) were crossed as female or male parent to conventional rice varieties (-/-), and the ratio of gusA positive (+/-) to negative (-/-) plants was investigated in test F1 population. When used as female parent, the segregation fit to 1:1, but significantly smaller than 1:1 when used as male parent. The seed-set of transgenic Nipponbare progeny was investigated individually for GUS positive and negative plants. It was found that the positive plants had an average seed-set of 64.5%, significantly lower than that of negative plants (77.9%). The biological and genetic basis of distorted segregation of transgenes was discussed and deduced on the basis of above results, and the authors are inclined to ascribe these phenomena to the poor competitive ability of pollens carrying transgenes.