In Arabidopsis, single genes encoding enzymes for the early reactions in the pathway have been identified. Mutations at these sites produce severe dwarf phenotypes. In contrast, small multigene families encode the dioxygenases. Interestingly, of the three enzymes, GA20ox, GA3ox and GA2ox , which participate in the later stages of the biosynthesis, the first two are encoded by a minimum of four and the last by at least five genes in Arabidopsis. The authors then review recent research on the regulation of gibberellin metabolism by development, hormones and light.
Several genes appear under tight developmental control.
Members of the dioxygenase gene families show tissue-specific patterns of expression. For example, in Arabidopsis, expression of the GA20ox1 and GA3ox1 genes occurs in growing vegetative tissues and in some flower organs. The authors elaborate also on the hormonal regulation of GA biosynthesis through the use of examples. Treatment of plants with bioactive GAs reduces the levels of transcripts for GA20ox and GA3ox genes. Some, but not all genes in the pathway are involved in negative feedback regulation.