Overlapping Yet Distinct Promoter Activities of Two Arabidopsis Genes Coding for Nearly Identical Isoforms of the Acyl Carrier Protein

Acyl carrier protein is encoded by at least five genes in Arabidopsis. Isoforms encoded by genes Acl1.2 and Acl1.3 differ by a single amino acid. We have examined the expression patterns directed by the Acl1.2 and Acl1.3 gene promoters in transgenic Arabidopsis using the reporter gene coding for ß-glucuronidase (GUS). Fluorometric and histochemical analyses showed that the two promoters have overlapping yet distinct patterns of activity in both vegetative and reproductive tissues. In germinating seeds, the Acl1.2 promoter directed expression in all tissues at 2 days after imbibition (DAI) and then gradually became restricted to the elongation zone of the root apex, the root-hypocotyl transition zone, shoot apex, and cotyledon vasculature by 6 DAI. Acl1.3 promoter down-regulation was evident only in the basal hypocotyl region during this same time period. In young plants, Acl1.2 promoter activity was restricted to apical regions and within lateral root primordia. In anthesis-stage flowers, Acl1.2 was expressed predominantly in the stigmatic papillae and mature pollen. Distinct expression profiles were also observed during embryogeny, where Acl1.2 activity declined prior to stages associated with cotyledon cell expansion and storage reserve deposition, whereas Acl1.3 promoter activity increased during this time. Overall, the Acl1.3 promoter exhibited a more constitutive pattern of expression when contrasted with Acl1.2, which tended to be expressed in meristematic or expanding tissues, and specific reproductive structures.