| Abstract: | Abstract Mechanism(s) of gene transformation and integration in rice (Oryza sauva L.) is/are not currently well understood. This research was conducted to determine whether a transgene is inserted into the rice genome specifically or randomly. Seven homozygous transgenic Taipei (T) 309 and Nipponbare plants with the bar transgene from different rice transformation events were crossed. The segregation of F2 and F3 populations from a total of 21 crosses was studied in a greenhouse and field to determine if the genes were allelic or non-allelic. Five genomic locations appeared to be involved among the seven transgenic plants. An additional 20 homozygous transgenic T309 plants, with the bar transgene from different transformation events, were crossed reciprocally with the previous seven plants. One hundred and fifteen crosses made during 1999 and 2000 were analyzed for allelism. In some combinations, the genes were allelic, but most of them were non-allelic, with two or more pairs of genes being expressed. Twenty loci among the 27 transgenic plants were involved and some plants had several inserted genes expressed. Genes in nine out of 27 transformed plants were allelic. We concluded that the functional foreign (bar) gene was restrictively/preferentially inserted into the rice genome in some cases and was not completely randomly inserted and expressed in the rice genome. If the mechanism(s) for preferential insertion were identified, rice researchers could possibly control insertion sites of transgenes to optimize gene expression. |
