Transposon mutagenesis of nuclear photosynthetic genes in Zea mays

William B. Cook, Donald Miles

The discovery of a new maize (Zea mays L.) transposon system, Mutator, and the cloning of the 1.4 kilobase transposon, Mul, have made feasible the isolation of nuclear photosynthetic genes which are recognized only by their mutant phenotype. Mutant maize plants which express a high chlorophyll fluorescent (hcf) phenotype due to a defect in the electron transport or photophosphorylation apparatus have been isolated following mutagenesis with an active Mutator stock. The affected genes and their products in these mutants are inaccessible to classical methods of analysis. However, mutagenesis with the Mutator transposon makes it possible to isolate these genes.Although the PSII-deficient mutant hcf3 has been thoroughly studied by classical photo-biological methods, the nature of the lesion which results in the observed phenotype has not been established. A Mutator-induced allele of hcf3 has been isolated. A fragment of genomic DNA has been identified which is homologous to Mul and co-segregates with the mutant phenotype. This fragment is expected to contain a portion of the hcf3 locus which will be used to clone the normal gene. Direct study of the gene can provide insight into the nature and function of its polypeptide product.This approach can be used to study any photosynthetic gene which has been interrupted by a transposon. The isolation of more than 100 different chemically-induced hcf mutants, most of which can not be fully characterized using classical means, indicates the wealth of information which can be obtained using a transposon tagging technique.