IDENTIFICATION OF DOMAINS IN AN ARABIDOPSIS ACYL CARRIER PROTEIN GENEPROMOTER REQUIRED FOR MAXIMAL ORGAN-SPECIFIC EXPRESSION

Deletions were made in the promoter of the acyl carrier protein (ACP) Acll.2 gene from Arabidopsis to investigate the nature of the cis-acti ng elements that direct its expression. These constructs, which includ ed the untranslated leader region, were fused to a reporter gene codin g for beta-glucuronidase (GUS) and transformed into tobacco. Quantitat ive fluorometric analysis of GUS activity in transgenic plants showed that expression in young leaves drops to a basal level when a 85 bp do main, from -320 to -236 relative to transcription initiation, is delet ed. Maximum promoter activity in roots also depends on this domain, bu t two other regions are also important. In total, deletion of the sequ ences from -466 to -55 caused an ca. 80-fold reduction in Acll.2 promo ter activity in roots. The -320 to -236 domain forms a complex with a protein factor found in leaves and roots, which was not detectable in seeds. The formation of this protein-DNA complex was abolished by muta tion of a bZIP core motif, ACGT, found within the context AAGACGTAG, w hich is dissimilar to the other bZIP-binding sites thus far characteri zed in plants. Previously we showed that Acll.2 promoter activity is h ighest in seeds [2]. Here we find, in contrast to leaves and roots, th at deletion to position -236 has no effect on GUS levels in seeds. How ever, nearly a 100-fold drop was observed when the -235 to -55 region was removed. Hence, this 180 bp domain contains all the cis-acting inf ormation necessary for Acll.2 promoter activity in seeds. The same reg ion is necessary for Acll.2 activity in the receptacle, stigma, tapetu m and pollen of the flower, as demonstrated by histochemical staining.