Volatile terpenoids and tropolones in heartwood extracts of yellow-cedar, Monterey cypress, and their hybrid Leyland cypress

International audienceKey message Leyland cypress, an intergeneric hybrid, produces the same volatile heartwood compounds as its parental taxa, yellow-cedar and Monterrey cypress. However, the proportion of total sesquiterpenes and some of the individual components appear unique to their respective heartwoods.ContextLeyland cypress, xHesperotropsis leylandii is an intergeneric hybrid between yellow-cedar, Callitropsis nootkatensis, and Monterey cypress, Hesperocyparis macrocarpa. Their heartwoods are protected by bioactive compounds and rated very durable to durable for products used above ground. Several compounds in yellow-cedar and Monterrey cypress heartwoods are also active against various fungi, bacteria, human insect pests, and plant pathogens, whereas Leyland cypress heartwood has never been thoroughly investigated.AimsThe first aim for this study was to examine the volatile compounds in ethyl acetate extracts from the heartwood of all three tree species in Oregon. The second aim was to determine the extent Leyland cypress differs from its parental species, and further investigate any of its novel compounds for biological activity.MethodsEthyl acetate extracts of fresh heartwood were prepared for three trees of each species and analyzed by gas chromatography.ResultsThirty-three compounds were detected at 0.5 % or greater abundance across all species, and 23 were identified. Carvacrol was the major monoterpene and nootkatin the most abundant tropolone in all three species. Valencene 11, 12-diol and nootkatone topped the list of sesquiterpenes in yellow-cedar and Leyland cypress, respectively, whereas no sesquiterpenes were detected in Monterrey cypress. This appears to be the first report of tropolones hinokitiol, procerin, and nootkatin in Leyland cypress, α-thujaplicinol, pygmaein, and procerin in Monterrey cypress, and hinokitiol in yellow-cedar.ConclusionsLeyland cypress heartwood does not biosynthesize structurally unique compounds from those produced by its parental species, and is an unlikely source of novel biocides. However, the proportion of total sesquiterpenes and some of the individual components in Leyland cypress heartwood may distinguish it from the heartwood of its parental species

A unique mechanism for methyl ester formation via an amide intermediate found in myxobacteria.

Secondary metabolism involves a broad diversity of biochemical reactions that result in a wide variety of biologically active compounds. Terminal amide formation during the biosynthesis of the myxobacterial electron-transport inhibitor, myxothiazol, was analyzed by heterologous expression of the unique nonribosomal-peptide synthetase, MtaG, and incubation with a synthesized substrate mimic. These experiments provide evidence that the terminal amide is formed from a carrier protein-bound myxothiazol acid that is thioesterified to MtaF. This intermediate is transformed to an amide by extension with glycine and subsequent oxidative cleavage by MtaG. The final steps of melithiazol assembly involve a highly similar protein-bound intermediate (attached to MelF, a homologue of MtaF), which is transformed to an amide by MelG (homologue of MtaG). In this study, we also show that the amide moiety of myxothiazol A can be hydrolyzed in vivo to the formerly unknown free myxothiazol acid by heterologous expression of melJ in the myxothiazol producer Stigmatella aurantiaca DW4/3-1. The methyltransferase MelK can finally methylate the acid to give rise to the methyl ester, which is produced as the final product in the melithiazol A biosynthetic pathway. These experiments clarify the role of MelJ and MelK during melithiazol assembly