Gibberellin Biosynthesis in Higher Plants

Biosynthesis of the major biologically active gibberellins (GAs) in higher plants proceeds first in plastids via the tetracyclic diterpene hydrocarbon ent-kaurene, which is oxidised by membrane-associated cytochrome P450 mono-oxygenases to produce GA(12) and GA(53) on the endoplasmic reticulum. These intermediates are oxidised further by the soluble 2-oxoglutarate-dependent dioxygenases GA 20-oxidase and GA 3-oxidase to the active C-19-GA end products, GA(4) and GA(1), respectively. The genes encoding most of the enzymes of the pathway have been identified in several species and the mechanisms by which their expression is regulated in response to developmental and environmental signals are being elucidated. The chapter will review the pathway, discuss the function of the biosynthetic enzymes and highlight recent understanding of their regulation.