Variation in the inheritance of expression among subclones for unselected (uidA) and selected (bar) transgenes in maize (Zea mays L.).

Variation in the inheritance of expression among subclones for an unselected (uidA) and a selected (bar) transgene was analyzed in two individual transformation events in maize. The unselectable gene (uidA) and the selectable gene (bar), on two separate plasmids, were transferred to maize (Hi-II derivative) by particle bombardment of embryogenic calli or suspension cells. A total of 188 fertile T1 plants were obtained from one transformant (transformation event BG which integrated uidA and bar). A total of 98 fertile T1 plants were obtained from a second transformant (transformation event B which integrated bar). Through self-pollination and/or cross-pollination in the greenhouse, approximately 10 000 T2 progeny were obtained from event BG, and more than 1000 T2 progeny were obtained from event B. Segregation of transgene expression was analyzed statistically in a total of 2350 T2 progeny from 40 T1 subclones of event BG and in 217 T2 progeny from six T1 subclones from event B. Variation in the inheritance of expression among subclones for the two transgenes (uidA and bar) was observed in the two transformants. A significant difference was observed between the use of the female or male as the transgenic parent in the inheritance of expression for the two transgenes in event BG. No inheritance through the pollen was observed in two of four T1 subclones analyzed in event B. Co-expression analysis of event BG showed that both transgenes were co-expressed in 67.7% of the T2 plants which expressed at least one of the two transgenes. Of the T2 expressing plants, 30.4% expressed only bar, and 1.9% expressed only uidA. Inactivation of the unselected (uidA) and the selected (bar) transgenes was observed in individual T2 plants.