Promoter elements required for developmental expression of the maize Adh1 gene in transgenic rice.
To define the regions of the maize alcohol dehydrogenase 1 (Adh1) promoter that confer tissue-specific expression, a series of 5' promoter deletions and substitution mutations were linked to the Escherichia coli beta-glucuronidase A (uidA) reporter gene and introduced into rice plants. A region between -140 and -99 not only conferred anaerobically inducible expression in the roots of transgenic plants but was also required for expression in the root cap, embryo, and in endosperm under aerobic conditions. GC-rich (GC-1, GC-2, and GC-3) or GT-rich (GT-1 and GT-2) sequence motifs in this region were necessary for expression in these tissues, as they were in anaerobic expression. Expression in the root cap under aerobic conditions required all the GC- and GT-rich motifs. The GT-1, GC-1, GC-2, and GC-3 motifs, and to a lesser extent the GT-2 motif, were also required for anaerobic responsiveness in rice roots. All elements except the GC-3 motif were needed for endosperm-specific expression. The GC-2 motif and perhaps the GT-1 motif appeared to be the only elements required for high-level expression in the embryos of rice seeds. Promoter regions important for shoot-, embryo-, and pollen-specific expression were proximal to -99, and nucleotides required for shoot-specific expression occurred between positions -72 and -43. Pollen-specific expression required a sequence element outside the promoter region, between +54 and +106 of the untranslated leader, as well as a silencer element in the promoter between -72 and -43.