The gibberellin 13-oxidase that specifically converts gibberellin A9 to A20 in Tripterygium wilfordii is a 2-oxoglutarate-dependent dioxygenase.

Abstract

A novel GA13-oxidase ofTripterygium wilfordii, TwGA13ox, is a 2-oxoglutarate-dependent dioxygenase. It specifically catalyzes the conversion of GA9to GA20, but not GA4to GA1. Gibberellins (GAs) play essential roles in plant growth and development. Previous characterization of GA20- and GA3-oxidases yielded a large number of genetic elements that can interconvert different GAs. However, enzymes that catalyze the 13-hydroxylation step are rarely identified. Here, we report that the GA13-oxidase of Tripterygium wilfordii, TwGA13ox, is a 2-oxoglutarate-dependent dioxygenase instead of reported cytochrome P450 oxygenases, among 376 differential proteins in comparative proteomics. Phylogenetic analysis showed that the enzyme resides in its own independent branch in the DOXC class. Unexpectedly, it specifically catalyzes the conversion of GA9 to GA20, but not GA4 to GA1. Contrary to the previous research, TwGA13ox transcriptional expression was upregulated ~ 146 times by exogenous application of methyl jasmonate (MeJA). RNAi targeting of TwGA13ox in T. wilfordii led to an 89.9% decrease of triptolide, a diterpenoid epoxide with extensive anti-inflammatory and anti-tumor properties. In subsequent MeJA supplementation experiments, triptolide production increased 13.4-times. TwGA13ox displayed root-specific expression. Our results provide a new GA13-oxidase from plants and elucidate the metabolic associations within the diterpenoid biosynthetic pathway (GAs, triptolide) at the genetic level.