A visible marker for antisense mRNA 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 conversion of glutamate to delta-aminolevulinate of which eight molecules are needed to synthesize a chlorophyll molecule. Two full-length cDNA clones that probably represent the homeologous Gsa genes of the two tobacco (Nicotiana tabacum) genomes have been isolated. The deduced amino acid sequences of the 468-residue-long precursor polypeptides differ by 10 amino acids. The cDNA sequence of isoenzyme 2 was inserted in reverse orientation under the control of a cauliflower mosaic virus 35S promoter derivative in an expression vector and was introduced by Agrobacterium-mediated transformation into tobacco plants. Antisense gene expression decreased the steady-state mRNA level of glutamate 1-semialdehyde aminotransferase, the translation of the enzyme, and chlorophyll synthesis. Remarkably, partial or complete suppression of the aminotransferase mimics in tobacco a wide variety of chlorophyll variegation patterns caused by nuclear or organelle gene mutations in different higher plants. The antisense gene is inherited as a dominant marker.