A homologous expression system for cloned zein genes.

Expression of the genes encoding the 10-, 15-, and 27-kDa zeins is maintained in suspension cultures derived from developing endosperm tissue of maize (Zea mays L.). Although expression of these genes is reduced in endosperm cultures as compared with that in endosperm tissue from developing kernels, it remains specific to the origin of explant, since no transcripts are detected in leaf tissue-derived suspension cultures. Transcript sizes are identical to those in developing seed endosperm tissue. Furthermore, accurate transcription initiation of the 10- and 27-kDa zein genes is observed by S1 nuclease mapping. Protoplasts isolated from endosperm cultures are capable of expressing foreign genes when transfected by electroporation. We demonstrate that the 5' flanking sequences of the 10- and 27-kDa zein genes are capable of promoting chloramphenicol acetyltransferase (CAT) gene expression in these transfected protoplasts. Our observations show that these maize endosperm cultures can be used as an efficient homologous system to study transcriptional regulation of zein genes.