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キーワード:
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要旨:
Volatiles are often released upon herbivory as plant defense compounds. While the formation of
volatiles above-ground has been intensively studied, little is known about herbivore-induced root
volatiles. Here, we show that cockchafer larvae-damaged roots of Populus trichocarpa and P. nigra
release a mixture of monoterpenes, including (−)-α-pinene, (−)-camphene, (−)-β-pinene, p-cymene,
and 1,8-cineole. Three terpene synthases, PtTPS16 and PtTPS21 from P. trichocarpa and PnTPS4
from P. nigra, could be identified and characterized in vitro. PnTPS4 was found to produce 1,8-cineole
as sole product. PtTPS16 and PtTPS21, although highly similar to each other, showed different
product specificities and produced γ-terpinene and a mixture of (−)-camphene, (−)-α-pinene,
(−)-β-pinene, and (−)-limonene, respectively. Four active site residues were found to determine the
different product specificities of the two enzymes. The expression profiles of PtTPS16, PtTPS21, and
PnTPS4 in undamaged and herbivore-damaged poplar roots generally matched the emission pattern
of monoterpenes, indicating that monoterpene emission in roots is mainly determined at the gene
transcript level. Bioassays with Phytophtora cactorum (Oomycetes) revealed inhibitory effects of vaporphase
1,8-cineole and (−)-β-pinene on the growth of this important plant pathogen. Thus herbivoreinduced
volatile monoterpenes may have a role in defense against pathogens that cause secondary
infections after root wounding.
