Characterization of diterpene synthase genes in Brachypodium distachyon, a monocotyledonous model plant, provides evolutionary insight into their multiple homologs in cereals.

Gibberellins are diterpenoid phytohormones that regulate plant growth, and are biosynthesized from a diterpene intermediate, ent-kaurene, which is produced from geranylgeranyl diphosphate via ent-copalyl diphosphate (ent-CDP). The successive two cyclization reactions are catalyzed by two distinct diterpene synthases, ent-CDP synthase (ent-CPS) and ent-kaurene synthase (KS). Various diterpene synthase genes involved in specialized metabolism were likely created through duplication and neofunctionalization of gibberellin-biosynthetic ent-CPS and KS genes in crops. Brachypodium distachyon is a monocotyledonous species that is a model plant in grasses. We herein found one ent-CPS gene homolog BdCPS and four tandemly-arrayed KS like genes BdKS1, KSL2, KSL3 and KSL4 in the B. distachyon genome, a simpler collection of paralogs than in crops. Phylogenetic and biochemical analyses showed that BdCPS and BdKS1 are responsible for gibberellin biosynthesis. BdKSL2 and BdKSL3 are suggested to be involved in specialized diterpenoid metabolism. Moreover, we restored KS activity of BdKSL2 through amino acid substitution.