Characterization of cis-regulatory regions responsible for developmental regulation of the gibberellin biosynthetic gene GA1 in Arabidopsis thaliana.

The Arabidopsis GA1 gene encodes copalyl diphosphate synthase, which catalyzes the first committed step in the gibberellin biosynthetic pathway. Previous studies indicated that the expression pattern of the GA1 gene is tissue-specific and cell-type-specific during development. Here we showed that expression of GA1 cDNA driven by the 2.4 kb 5'-upstream sequence plus the GA1 genomic coding region into the third exon was able to rescue the gal-3 mutant phenotype. To understand the mechanism controlling GA1 gene expression, cis-regulatory regions in the GA1 promoter were identified by promoter deletion analysis with the GA1-beta-glucuronidase (GUS) gene fusion system. The second intron and the region from -1391 to -997, with respect to the translation initiation site, positively regulate overall GA1-GUS expression level in all tissues examined. Several additional regulatory regions are involved in GA1-GUS expression in all the stages except in seeds: two positive regulatory regions in the first intron and the sequence between -425 and -207, and a negative regulatory region between -1848 and -1391. We also found that the region between -997 and -796 is essential for a high level of GA1 expression in developing seeds.