Dear Editor,Most of the plant hormones found in flowering plants contribute to growth regulation in the moss Physcomitrella patens.This moss does not produce gibberellin (GA) (Figure 1A).An entkaurene synthase (PpCPS/KS) and an ent-kaurene oxidase (PpKO) have been identified in P.patens,but in contrast to flowering plants,P.patens has no ent-kaurenoic acid oxidase (KAO) homologs (Hayashi et al.,2010;Miyazaki et al.,2011,Figure 1A).Nevertheless,several 2-oxoglutarate-dependent dioxygenase (2ODD) genes,which might be related to the GA synthesis pathway,have been annotated (Hirano et al.,2007),and ent-kaurene-deficient P.patens mutants (Ppcps/ks) showed limited protonemal cell differentiation of chloronemata to caulonemata,which are fast-growing cells that produce gametophores.The application of ent-kaurenoic acid (KA),but not GA,recovered the phenotype.These results support that P.patens lacks a GA biosynthetic pathway downstream of KA,indicating that KA metabolite(s) instead of GA may play physiological roles in P.patens.