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Abstract:
Key message Conifers contain P450 enzymes from the CYP79 family that are involved in cyanogenic glycoside
biosynthesis.
Abstract Cyanogenic glycosides are secondary plant compounds
that are widespread in the plant kingdom. Their biosynthesis
starts with the conversion of aromatic or aliphatic
amino acids into their respective aldoximes, catalysed by
N-hydroxylating cytochrome P450 monooxygenases (CYP)
of the CYP79 family. While CYP79s are well known in
angiosperms, their occurrence in gymnosperms and other plant divisions containing cyanogenic glycoside-producing
plants has not been reported so far. We screened the transcriptomes
of 72 conifer species to identify putative CYP79
genes in this plant division. From the seven resulting fulllength
genes, CYP79A118 from European yew (Taxus baccata)
was chosen for further characterization. Recombinant
CYP79A118 produced in yeast was able to convert l-tyrosine,
l-tryptophan, and l-phenylalanine into p-hydroxyphenylacetaldoxime,
indole-3-acetaldoxime, and phenylacetaldoxime,
respectively. However, the kinetic parameters of the
enzyme and transient expression of CYP79A118 in Nicotiana
benthamiana indicate that l-tyrosine is the preferred
substrate in vivo. Consistent with these findings, taxiphyllin,
which is derived from l-tyrosine, was the only cyanogenic
glycoside found in the different organs of T. baccata. Taxiphyllin
showed highest accumulation in leaves and twigs,
moderate accumulation in roots, and only trace accumulation
in seeds and the aril. Quantitative real-time PCR revealed
that CYP79A118 was expressed in plant organs rich in taxiphyllin.
Our data show that CYP79s represent an ancient family of plant P450s that evolved prior to the separation of
gymnosperms and angiosperms. CYP79A118 from T. baccata
has typical CYP79 properties and its substrate specificity
and spatial gene expression pattern suggest that the
enzyme contributes to the formation of taxiphyllin in this plant species.
