OVERLAPPING YET DISTINCT PROMOTER ACTIVITIES OF 2 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 beta-glucuronidase (GUS). Fluorometric and histochemi cal analyses showed that the two promoters have overlapping yet distin ct patterns of activity in both vegetative and reproductive tissues. I n germinating seeds, the Acl1.2 promoter directed expression in all ti ssues at 2 days after imbibition (DAI) and then gradually became restr icted to the elongation zone of the root apex, the root-hypocotyl tran sition zone, shoot apex, and cotyledon vasculature by 6 DAI. Acl1.3 pr omoter down-regulation was evident only in the basal hypocotyl region during this same time period. In young plants, Acl1.2 promoter activit y was restricted to apical regions and within lateral root primordia. In anthesis-stage flowers, Acl1.2 was expressed predominantly in the s tigmatic 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 reserv e deposition, whereas Acl1.3 promoter activity increased during this t ime. Overall, the Acl1.3 promoter exhibited a more constitutive patter n of expression when contrasted with Acl1.2, which tended to be expres sed in meristematic or expanding tissues, and specific reproductive st ructures.