The first step of gibberellin biosynthesis in pumpkin is catalyzed by at least two copalyl diphosphate synthases encoded by differentially regulated genes

摘要

The first step in gibberellin biosynthesis is catalysed by copalyl diphosphate synthase (CPS) and ent-kaurene synthase. Two cDNAs, CmCPS1 and CmCPS2, were cloned from pumpkins (Cucurbita maxima) that each encode a CPS. Both recombinant fusion CmCPSproteins were active in vitro. CPS were translocated into plastids and processed by cleavage of transit peptides. For CmCPS1 and CmCPS2, the putative transit peptides cannot exceed the first 99 and 107 amino acids, respectively, because longer N-terminaldeletions abolished activity. Levels of both CmCPS transcripts were strictly regulated in an organ-specific and developmental manner. Both transcripts were almost undetectable in leaves and were abundant in petioles. CmCPS1 transcript levels were high in young cotyledons and low in roots. In contrast, CmCPS2 transcripts were undetectable in cotyledons but present at significant levels in roots. In hypocotyls, apices and petioles, CmCPS1 transcript levels decreased with age much more rapidly than thoseof CmCPS2. It is speculated that CmCPS1 expression is correlated with the early stages of organ development, whereas CmCPS2 expression is correlated with subsequent growth. In contrast, C. maxima ent-kaurene synthase transcripts were detected in every organ at almost constant levels. Thus, ent-kaurene biosynthesis may be regulated through control of CPS expression.