Mendelian transmission of genes introduced into plants by the Ti plasmids of Agrobacterium tumefaciens.

Insertion of the bacterial transposon Tn7 was used to obtain mutants of an octopine Ti plasmid. Crown gall tumours induced on tobacco by an Agrobacterium tumefaciens strain carrying a particular mutant Ti plasmid (pGV2100) were found to give rise to shoots. These shoots were grown in vitro and one of them (rGV-1) was found to contain the T-DNA specific enzyme lysopine dehydrogenase (LpDH) and to form roots. After transfer to soil, rGV-1 developed into a morphologically and functionally normal tobacco plant. All cells of the regenerant and of vegetatively produced offspring were shown, by cloning of leaf protoplasts, to contain T-DNA and LpDH activity, rGV-1 and vegetatively produced offspring flowered normally. Plantlets obtained from haploid anther cultures were tested for LpDH activity. Forty-one percent of these plantlets were LpDH positive. Moreover, both self-pollination of rGV-1 and crosses between rGV-1 and normal tobacco plants showed that the LpDH character was transmitted both through the pollen and through the eggs of rGV-1 as a single dominant factor with Mendelian segregation ratios typical for monohybrid crosses. By repeated selfing, homozygous plants were obtained which bred true with respect to LpDH. The importance of these findings with respect to the use of Agrobacterium tumefaciens and Ti plasmids for genetic engineering in plants is discussed.