Plant Molecular Biology 18: 201-210, 1992. © 1992 Kluwer Academic Publishers. Printed in Belgium. 201 Segregation of transgenes in maize T. Michael Spencer, James V. O'Brien, William G. Start, Thomas R. Adams, William J. Gordon-Kamm, Peggy G. Lemaux 1 Discovery Research, DEKALB Plant Genetics, Eastern Point Road, Groton, CT 06340, USA; 1present address: Department of Plant Biology, University of California, Berkeley, CA 94720, USA Received 10 June 1991; accepted in revised form 30 August 1991 Key words: maize, transformation, inheritance, phosphinothricin acetyltransferase, cotransformation, microprojectile bombardment Abstract Progeny recovered from backcrossed transgenic maize tissue culture regenerants (R0) were analyzed to determine the segregation, expression, and stability of the introduced genes. Transgenic A188 x B73 R 0 plants (regenerated from embryogenic suspension culture cells transformed by microprojectile bombard- ment; see [9]) were pollinated with nontransformed B73 pollen. Inheritance of a selectable marker gene, bar, and a nonselectable marker gene, uidA, was analyzed in progeny (R1) representing four indepen- dent transformation events. Activity of the bar gene product, phosphinothricin acetyltransferase (PAT), was assessed in plants comprising the four R 1 populations. The number of R 1 plants containing PAT activity per total number of R1 plants recovered for each population was 2/7, 19/34, 3/14 and 73/73. Molecular analysis confirmed the segregation of bar in three R1 populations and the lack of segregation in one R1 population. Cosegregation analysis indicated genetic linkage of bar and uidA in all four R 1 populations. Analysis of numerous R2 plants derived from crossing transformed R 1 plants with non- transformed inbreds revealed 1:1 segregation of PAT activity in three of four lines, including the line that failed to segregate in the R 1 generation. Integrated copies of bar in one line appeared to be unstable or poorly transmitted. Introduction Major progress has been made in overcoming the recalcitrance of agronomically important mono- cots to genetic transformation. Rice yielded to transformation via protoplast-based, direct DNA uptake systems, ultimately giving rise to fertile transgenic japonica [17] and indica [4] rice plants. Recovery of fertile transgenic maize plants [ 9, 8 ] was recently accomplished using micropro- jectile bombardment, a direct DNA delivery sys- tem not requiring protoplast isolation [ 13]. While this progress is encouraging, very little is known about the integration and expression, and ulti- mately, the inheritance and stability of genes in- troduced into important monocots. Fertile transgenic plants have been recovered from numerous dicot species using Agro- bacterium-mediated transformation. Agrobacte- rium transformation of dicots usually results in a low number (average of 3 copies) of T-DNA in- sertions into the host plant genome. T-DNA in- sertions appear to be site-independent and are often unlinked (for review, see [22]). Inheritance