Reference "Identification of syn-pimara-7,15-diene synthase reveals functional clustering of terpene synthases involved in rice phytoalexin/allelochemical biosynthesis"

Reference ID

11690

Title

Identification of syn-pimara-7,15-diene synthase reveals functional clustering of terpene synthases involved in rice phytoalexin/allelochemical biosynthesis

Source

Plant physiology, 2004, vol. 135, pp. 2098-2105

Authors (5)

Wilderman-P-R	Xu-M
Jin-Y	Coates-R-M
Peters-R-J

Abstract

Rice (Oryza sativa) produces momilactone diterpenoids as both phytoalexins and
allelochemicals. Accordingly, the committed step in biosynthesis of these
natural products is catalyzed by the class I terpene synthase that converts syn-
copalyl diphosphate to the corresponding polycyclic hydrocarbon intermediate
syn-pimara-7,15-diene. Here, a functional genomics approach was utilized to
identify a syn-copalyl diphosphate specific 9beta-pimara-7,15-diene synthase
(OsDTS2). To our knowledge, this is the first identified terpene synthase with
this particular substrate stereoselectivity and, by comparison with the
previously described and closely related ent-copalyl diphosphate specific cassa-12,15-
diene synthase (OsDTC1), provides a model system for investigating the
enzymatic determinants underlying the observed difference in substrate
specificity. Further, OsDTS2 mRNA in leaves is up-regulated by conditions that
stimulate phytoalexin biosynthesis but is constitutively expressed in roots,
where momilactones are constantly synthesized as allelochemicals. Therefore,
transcription of OsDTS2 seems to be an important regulatory point for
controlling production of these defensive compounds. Finally, the gene
identified here as OsDTS2 has previously been mapped at 14.3 cM on chromosome
4. The class II terpene synthase producing syn-copalyl diphosphate from the
universal diterpenoid precursor geranylgeranyl diphosphate was also mapped to
this same region. These genes catalyze sequential cyclization steps in
momilactone biosynthesis and seem to have been evolutionarily coupled by
physical linkage and resulting cosegregation. Further, the observed correlation
between physical proximity and common metabolic function indicates that other
such class I and class II terpene synthase gene clusters may similarly catalyze
consecutive reactions in shared biosynthetic pathways.