Reference "Identification of a biosynthetic gene cluster in rice for momilactones"

Reference ID

11687

Title

Identification of a biosynthetic gene cluster in rice for momilactones

Source

The Journal of biological chemistry, 2007, vol. 282, pp. 34013-34018

Authors (13)

Shimura-K	Okada-A	Okada-K	Jikumaru-Y
Ko-K-W	Toyomasu-T	Sassa-T	Hasegawa-M
Kodama-O	Shibuya-N	Koga-J	Nojiri-H
Yamane-H

Abstract

Rice diterpenoid phytoalexins such as momilactones and phytocassanes are
produced in suspension-cultured rice cells treated with a chitin oligosaccharide
elicitor and in rice leaves irradiated with UV light. The common substrate
geranylgeranyl diphosphate is converted into diterpene hydrocarbon precursors
via a two-step sequential cyclization and then into the bioactive phytoalexins
via several oxidation steps. It has been suggested that microsomal cytochrome
P-450 monooxygenases (P-450s) are involved in the downstream oxidation of the
diterpene hydrocarbons leading to the phytoalexins and that a dehydrogenase is
involved in momilactone biosynthesis. However, none of the enzymes involved in
the downstream oxidation of the diterpene hydrocarbons have been identified. In
this study, we found that a putative dehydrogenase gene (AK103462) and two
functionally unknown P-450 genes (CYP99A2 and CYP99A3) form a chitin
oligosaccharide elicitor- and UV-inducible gene cluster, together with OsKS4 and
OsCyc1, the diterpene cyclase genes involved in momilactone biosynthesis.
Functional analysis by heterologous expression in Escherichia coli followed by
enzyme assays demonstrated that the AK103462 protein catalyzes the conversion of
3beta-hydroxy-9betaH-pimara-7,15-dien-19,6beta-olide into momilactone A. The
double knockdown of CYP99A2 and CYP99A3 specifically suppressed the elicitor-
inducible production of momilactones, strongly suggesting that CYP99A2, CYP99A3,
or both are involved in momilactone biosynthesis. These results provide strong
evidence for the presence on chromosome 4 of a gene cluster involved in
momilactone biosynthesis.