The majority of genes encoding gibberellin (GA) biosynthesis and deactivation enzymes have been identified to date. Recent studies have highlighted the occurrence of previously unrecognized deactivation mechanisms, including epoxidation and methylation. GA concentrations in plant tissues are carefully optimized by a number of internal and external signals. Studies have recently shown that, in many cases, bioactive GA levels are modulated through coordinated regulation of GA biosynthesis and deactivation. In addition, the identification of transcription factors that directly regulate GA biosynthesis and deactivation genes has started to uncover the molecular mechanisms for fine-tuning the hormone levels. In this article, I summarize our current understanding of the GA biosynthesis and deactivation pathways in plants, and discuss how the concentration of bioactive GAs is regulated in several selected systems.
