STRUCTURE AND FUNCTION OF SELECTABLE AND NON-SELECTABLE TRANSGENES INMAIZE AFTER INTRODUCTION BY PARTICLE BOMBARDMENT

Zea mays transformants produced by particle bombardment of embryogenic suspension culture cells of the genotype A188 x B73 and selected on k anamycin or bialaphos were characterized with respect to transgene int egration, expression, and inheritance. Selection on bialaphos, mediate d by the bar or par genes, was more efficient than selection on kanamy cin, mediated by the nptII gene. Most transformants contained multicop y, single locus, transgene insertion events. A transgene expression ca ssette was more likely to be rearranged if expression of that gene was not selected for during callus growth. Not all plants regenerated fro m calli representing single transformation events expressed the transg enes, and a nonselectable gene (uidA) was expressed in fewer plants th an was the selectable transgene. Mendelian inheritance of transgenes c onsistent with transgene insertion at a single locus was observed for approximately two thirds of the transformants assessed. Transgene expr ession was typically, but not always, predictable in progeny plants - transgene silencing, as well as poor transgene transmission to progeny , was observed in some plant lines in which the parent plants had expr essed the transgene.