HpDTC1, a Stress-Inducible Bifunctional Diterpene Cyclase Involved in Momilactone Biosynthesis, Functions in Chemical Defence in the Moss Hypnum plumaeforme.

Kazunori Okada,Sho Miyazaki,Ken-Ichiro Hayashi,Kaoru Fujiwara,Hiroshi Nozaki,Hisakazu Yamane,Honoka Kimura,Masahiro Natsume,Hideaki Nojiri,Yuki Hatano,Ryosuke Kainuma,Koji Miyamoto,Hiroshi Kawaide,Masatoshi Nakajima

doi:10.1038/srep25316

Abstract

Momilactones, which are diterpenoid phytoalexins with antimicrobial and allelopathic functions, have been found only in rice and the moss Hypnum plumaeforme. Although these two evolutionarily distinct plant species are thought to produce momilactones as a chemical defence, the momilactone biosynthetic pathway in H. plumaeforme has been unclear. Here, we identified a gene encoding syn-pimara-7,15-diene synthase (HpDTC1) responsible for the first step of momilactone biosynthesis in the moss. HpDTC1 is a bifunctional diterpene cyclase that catalyses a two-step cyclization reaction of geranylgeranyl diphosphate to syn-pimara-7,15-diene. HpDTC1 transcription was up-regulated in response to abiotic and biotic stress treatments. HpDTC1 promoter-GUS analysis in transgenic Physcomitrella patens showed similar transcriptional responses as H. plumaeforme to the stresses, suggesting that a common response system to stress exists in mosses. Jasmonic acid (JA), a potent signalling molecule for inducing plant defences, could not activate HpDTC1 expression. In contrast, 12-oxo-phytodienoic acid, an oxylipin precursor of JA in vascular plants, enhanced HpDTC1 expression and momilactone accumulation, implying that as-yet-unknown oxylipins could regulate momilactone biosynthesis in H. plumaeforme. These results demonstrate the existence of an evolutionarily conserved chemical defence system utilizing momilactones and suggest the molecular basis of the regulation for inductive production of momilactones in H. plumaeforme.

Highlights

H. plumaeforme is the only plant species known to produce momilactones
We identified a stress-inducible H. plumaeforme diterpene cyclase gene, HpDTC1promoter::GUS construct (HpDTC1), encoding syn-pimaradiene synthase, which catalyses key steps of momilactone biosynthesis to yield syn-pimara-7,15-diene from geranylgeranyl diphosphate (GGDP) via syn-copalyl diphospate (syn-CDP) as the reaction intermediate
HpDTC1 is a bifunctional enzyme consisting of type B cyclase that is responsible for syn-CDP synthesis and type A activity for syn-pimaradiene synthesis

Summary

Introduction

H. plumaeforme is the only plant species known to produce momilactones. We previously found that momilactones function as allelochemicals in this moss[1]. Momilactones in H. plumaeforme accumulate in response to various stresses, including UV irradiation and heavy metal treatment[10]. These studies suggest that momilactone production could be a defence reaction in H. plumaeforme, in addition to providing allelopathic activity against other plants. The expression of all genes in momilactone biosynthesis is coordinately induced in response to both biotic and abiotic stresses, including blast fungus infection and heavy metal treatment[4,14]. To dissect the biosynthetic pathway of momilactone and its regulatory mechanism in response to stress, we cloned the gene for syn-pimaradiene synthase (HpDTC1, H. plumaeforme diterpene cyclase 1), a key first step enzyme in momilactone biosynthesis. Our results aid in understanding the momilactone biosynthetic pathway in the moss and the molecular basis of an evolutionarily conserved chemical defence system between mosses and angiosperms utilizing momilactones

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Results

Conclusion