Gibberellin A1 Metabolism Contributes to the Control of Photoperiod-Mediated Tuberization in Potato
Figure 1
Major reactions in GA biosynthetic pathway and phylogenetic analysis of GA 3-oxidases.
(A) The pathway is classified into three groups based on the enzymatic activity and subcellular localization. Plastidial terpene cyclases convert the precursor geranylgeranyl diphosphate (GGDP) into ent-copalyl diphosphate (CDP), and subsequently into ent-kaurene, in a two-step process catalyzed by ent-copalyl diphosphate synthase (CPS) and ent-kaurene synthase (KS). Cytochrome P-450 mono-oxygenases such as ent-kaurene oxidase (KO), ent-kaurenoic acid oxidase (KAO) yield GA12. Cytoplasmic dioxygenases are responsible for the latest steps and conversion to bioactive gibberellins and their inactive catabolites. GA12 in potato is early 13-hydroxylated by GA 13-oxidase (GA13ox). As indicated by curved dotted T-lines or arrows emerging from the bioactive GA1, GA20ox and GA3ox corresponding transcripts are under negative feed-back regulation, whereas GA2ox mRNA is under positive feed-forward regulation by GA1. (B) Neighbor-joining tree obtained with the alignment of the amino acid sequences: St3ox1 and St3ox2 correspond to potato StGA3ox1 (FJ792644) and StGA3ox2 (FJ792643); At3ox1 and At3ox2 to arabidopsis AtGA3ox1 (NM101424) and AtGA3ox2 (NM106683); Ps3ox1 to pea PsGA3ox1 (AF010167), Ls3h1 and Ls3h2 to lettuce LsGA3ox1 (AB012205) and LsGA3ox2 (AB012206); Le3ox1 and Le3ox2 to tomato SlGA3ox1 (AB010991) and SlGA3ox2 (AB010992), tobacco Nty is NtGA3ox1 (AB032198), and Os3ox1 and Os3ox2 are rice genes OsGA3ox1 and OsGA3ox2 (AB054084 and AB056519).