Sexual transmission of T-DNA in abnormal tobacco regenerants transformed by octopine and nopaline strains of Agrobacterium tumefaciens

Abstract

Transformed shoots regenerating from Crown gall tissues were produced by in vitro infection of regenerating tobacco protoplasts with Agrobacterium tumefaciens. As these shoots were abnormal in their growth and were unable to form roots, they were grafted onto normal tobacco, resulting in the formation of flowering shoots. Sexual crosses between different grafts and selfing produced two different types of seedlings. Some developed into normal, untransformed plants whereas others failed to develop a root system and remained very small. The abnormal seedlings were shown to consist of transformed cells since they expressed the opine marker. The suppression of root formation and the production of opines were 100 percent linked. The analysis of the progeny indicated that the shoots derived from these tumour lines were hemizygous for the T-DNA linked genes and expressed these genes as a dominant locus. The opine-positive shoots were shown to contain a deleted T-DNA and also some T-DNA specific transcripts: the transcript for octopine synthase or LpDH and two other transcripts, one of which is known to be involved in the suppression of root formation. The same transcripts could also be detected in the sexual progeny. These observations confirm that some active tumour-controlling genes can be sexually transmitted and do not drastically interfere with seed development, germination and early shoot formation. The formation of roots by these seedlings is however severely suppressed.