Identification of a promoter sequence from the BETL1 gene cluster able to confer transfer-cell-specific expression in transgenic maize

The maize (Zea mays L.) betl1 locus, encoding a basal endosperm transfer la yer-specific protein, has been mapped and molecularly cloned in its entiret y. The locus is shown to consist of three gene copies in the maize inbred l ine A69Y. To distinguish the three transcription units from the locus name, we have termed them BETL1a, BETL1b, and BETL1c. Two of the copies are expr essed, whereas one is inactive and contains retrotransposon-like insertions in both promoter and intron regions. Based on this information, and a rest riction site map covering 17 kb around the BETL1 locus, a DNA fragment puta tively containing an active promoter sequence was identified, This fragment was tested for its ability to confer transfer-cell-specific expression in transient and stably transformed maize tissues. The transgenic maize plants obtained showed the predicted cell-type specificity of expression restrict ed to the basal endosperm transfer cells, although there were minor deviati ons in promoter strength and timing and accumulation of the transgene produ ct from the corresponding BETL-1 endogene expression pattern.