A VISIBLE MARKER FOR ANTISENSE MESSENGER-RNA EXPRESSION IN PLANTS - INHIBITION OF CHLOROPHYLL SYNTHESIS WITH A GLUTAMATE-1-SEMIALDEHYDE AMINOTRANSFERASE ANTISENSE GENE

Glutamate 1-semialdehyde aminotransferase [(S)-4-amino-5-oxopentanoate 4,5-aminomutase, EC 5.4.3.8] catalyzes the last step in the conversio n of glutamate to S-aminolevulinate of which eight molecules are neede d to synthesize a chlorophyll molecule. Two full-length cDNA clones th at probably represent the homeologous Gsa genes of the two tobacco (Ni cotiana tabacum) genomes have been isolated. The deduced amino acid se quences of the 468-residue-long precursor polypeptides differ by 10 am ino acids. The cDNA sequence of isoenzyme 2 was inserted in reverse or ientation under the control of a cauliflower mosaic virus 35S promoter derivative in an expression vector and was introduced by Agrobacteriu m-mediated transformation into tobacco plants. Antisense gene expressi on decreased the steady-state mRNA level of glutamate 1-semialdehyde a minotransferase, the translation of the enzyme, and chlorophyll synthe sis. Remarkably, partial or complete suppression of the aminotransfera se mimics in tobacco a wide variety of chlorophyll variegation pattern s caused by nuclear or organelle gene mutations in different higher pl ants. The antisense gene is inherited as a dominant marker.