hide
Free keywords:
-
Abstract:
Background: Amino acid-derived aldoximes and nitriles play important roles in plant defence. They are well-known
as precursors for constitutive defence compounds such as cyanogenic glucosides and glucosinolates, but are also
released as volatiles after insect feeding. Cytochrome P450 monooxygenases (CYP) of the CYP79 family catalyze the
formation of aldoximes from the corresponding amino acids. However, the majority of CYP79s characterized so far
are involved in cyanogenic glucoside or glucosinolate biosynthesis and only a few have been reported to be
responsible for nitrogenous volatile production.
Results: In this study we analysed and compared the jasmonic acid-induced volatile blends of two Erythroxylum species,
the cultivated South American crop species E. coca and the African wild species E. fischeri. Both species produced different
nitrogenous compounds including aliphatic aldoximes and an aromatic nitrile. Four isolated CYP79 genes (two from each
species) were heterologously expressed in yeast and biochemically characterized. CYP79D62 from E. coca and CYP79D61
and CYP79D60 from E. fischeri showed broad substrate specificity in vitro and converted L-phenylalanine, L-isoleucine,
L-leucine, L-tryptophan, and L-tyrosine into the respective aldoximes. In contrast, recombinant CYP79D63 from E. coca
exclusively accepted L-tryptophan as substrate. Quantitative real-time PCR revealed that CYP79D60, CYP79D61, and
CYP79D62 were significantly upregulated in jasmonic acid-treated Erythroxylum leaves.
Conclusions: The kinetic parameters of the enzymes expressed in vitro coupled with the expression patterns of the
corresponding genes and the accumulation and emission of (E/Z)-phenylacetaldoxime, (E/Z)-indole-3-acetaldoxime,
(E/Z)-3-methylbutyraldoxime, and (E/Z)-2-methylbutyraldoxime in jasmonic acid-treated leaves suggest that CYP79D60,
CYP79D61, and CYP79D62 accept L-phenylalanine, L-leucine, L-isoleucine, and L-tryptophan as substrates in vivo and
contribute to the production of volatile and semi-volatile nitrogenous defence compounds in E. coca and E. fischeri.
