Unique and overlapping expression patterns of Arabidopsis CYP85 genes involved in brassinosteroid C-6 oxidation

Brassinosteroids (BRs) are steroid hormones that are essential for plant growth and development. To gain insight into potential sites of BR synthesis, we studied promoter activities of the two Arabidopsis BR C-6 oxidase genes (CYP85A1 and CYP85A2) in transgenic plants carrying promoter fusions with the GUS, GFP or LUC reporter genes. BR-dependent feedback regulation of the GUS reporter constructs indicated that their expression corresponded to those of the native genes. Both the CYP85A1 and CYP85A2 promoters showed maximum activity during the first week following germination, particularly in the vascular tissues. Compared to CYP85A2, CYP85A1 expression was weaker and confined to the early stages of seedling development. Stronger CYP85A2 promoter activity was evident in both juvenile and adult plants. Comparison of the 5-UTR and TATA box sequences of CYP85A1 and CYP85A2 revealed high homology, indicating a relatively recent gene duplication. We also found that transgenic Arabidopsis plants harbouring the tomato DWARF promoter-GUS fusion had similarities in the expression pattern to the Arabidopsis genes suggesting common transcriptional regulation of CYP85 genes in the two species.