Herbivore‐induced poplar cytochrome P450 enzymes of the CYP71 family convert aldoximes to nitriles which repel a generalist caterpillar

Abstract

SUMMARYNumerous plant species emit volatile nitriles upon herbivory, but the biosynthesis as well as the relevance of these nitrogenous compounds in plant-insect interactions remains unknown. Populus trichocarpa has been shown to produce a complex blend of nitrogenous volatiles, including aldoximes and nitriles, after herbivore attack. The aldoximes were previously reported to be derived from amino acids by the action of cytochrome P450 enzymes of the CYP79 family. Here we show that nitriles are derived from aldoximes by another type of P450 enzyme in P. trichocarpa. First, feeding of deuterium-labeled phenylacetaldoxime to poplar leaves resulted in incorporation of the label into benzyl cyanide, demonstrating that poplar volatile nitriles are derived from aldoximes. Then two P450 enzymes, CYP71B40v3 and CYP71B41v2, were characterized that produce aliphatic and aromatic nitriles from their respective aldoxime precursors. Both possess typical P450 sequence motifs but do not require added NADPH or cytochrome P450 reductase for catalysis. Since both enzymes are expressed after feeding by gypsy moth caterpillars, they are likely to be involved in herbivore-induced volatile nitrile emission in P. trichocarpa. Olfactometer experiments showed that these volatile nitriles have a strong repellent activity against gypsy moth caterpillars, suggesting they play a role in induced direct defense against poplar herbivores.

Identification and functional analysis of two P450 enzymes of Gossypium hirsutum involved in DMNT and TMTT biosynthesis

“…The expression of GhCYP82L s in G. hirsutum was significantly up‐regulated after herbivore damage, especially in leaves and stems. These results were consistent with those of ZmCYP92C s in Z. mays , PtCYP79D s in Populus trichocarpa and AtCYP82G1 in A. thaliana , which were strongly up‐regulated in herbivore‐damaged plants compared to undamaged controls (Irmisch et al ., ; Lee et al ., ; Richter et al ., ). The highly expressed GhCYP82L s contributed to the formation of homoterpenes in herbivore‐damaged plants.…”

The bifurcation of the cyanogenic glucoside and glucosinolate biosynthetic pathways

“…The CYP71E1‐catalyzed dehydration reaction converting Z‐oxime into the corresponding nitrile in sorghum, and by other CYP71 clan enzymes in other cyanogenic plants (Jørgensen et al ., ; Takos et al ., ), is an unusual reaction for a P450 to catalyze because these are known and classified as monooxygenases. However, a similar reaction has been reported for a P450 present in human and rat liver (DeMaster et al ., ; Boucher et al ., ; Hart‐Davis et al ., ), for CYP71B40 and CYP71B41 in poplar (Irmisch et al ., ) and for CYP71A13 involved in camalexin biosynthesis in A. thaliana (Nafisi et al ., ; Klein et al ., ). Other members of the large CYP71 family function as typical monooxygenases.…”

Flavan-3-ols Are an Effective Chemical Defense against Rust Infection

“…Although the biosynthesis and antiherbivore activity of these compounds have recently come under close scrutiny (Barbehenn and Constabel, 2011;Boeckler et al, 2013Boeckler et al, , 2014Irmisch et al, 2013Irmisch et al, , 2014, it is still not known if any are effective defenses against pathogens of various lifestyles.…”