Volatiles modulate the development of plant pathogenic rust fungi.

Rust fungi are obligate biotrophic pathogens that differentiate a series of specialized cells to establish infection. One of these cells, the haustorium, which serves to absorb nutrients from living host cells, normally develops only in planta. Here, we show that the rust fungus Uromyces fabae (Pers.) Schroet. stimulates volatile emission of its host, broad bean (Vicia faba L.). Volatiles were identified and shown to be perceived by the fungus in in vitro assays that excluded the host. Three of them, nonanal, decanal, and hexenyl acetate promoted the development of haustoria on artificial membranes. In contrast, the terpenoid farnesyl acetate suppressed this differentiation. In assays using whole plants, farnesyl acetate reduced rust disease not only on broad bean but also on several cereals and legumes including soybean. This natural substance was effective against all rusts tested when directly applied to the host. This demonstrated that farnesyl acetate may serve as a powerful novel tool to combat rust fungi including Phakopsora pachyrhizi that currently threatens the production of soybeans world-wide.

Dynamic pathway allocation in early terpenoid biosynthesis of stress-induced lima bean leaves.

Two independent pathways contribute in higher plants to the formation of isopenteny1 diphosphate (IDP), the central building block of isoprenoids. In general, the cytosolic mevalonate pathway (MVA) provides the precursors for sesquiterpenes and sterols, whereas the plastidial methylerythritol pathway (MEP) furnishes the monoterpene-, diterpene- and carotenoids. Administration of deuterium labeled 1-deoxy-d-xylulose and mevalolactone to lima beans (Phaseolus lunatus), followed by gas chromatographic separation and mass spectrometric analysis of de novo produced volatiles revealed that the strict separation of both pathways does not exist. This could be confirmed by blocking the pathways individually with cerivastatin((R)) (MVA) and fosmidomycin (MEP), respectively. Isotopic ratio mass spectrometry (IRMS) at natural abundance levels demonstrated independently and without the need for labeled precursors a dynamic allocation of the MVA- or the MEP-pathway in the biosynthesis of the nerolidol-derived homoterpene 4,8-dimethy1-nona-1,3,7-triene (DMNT). Insect-feeding upregulated predominantly the MVA-pathway, while the fungal elicitor alamethicin stimulated the biosynthesis of DMNT via the MEP-pathway.

Feeding of [5,5-2H(2)]-1-desoxy-D-xylulose and [4,4,6,6,6-2H(5)]-mevalolactone to a geosmin-producing Streptomyces sp. and Fossombronia pusilla.

The biosynthesis of the trisnor sesquiterpenoid geosmin (4,8a-dimethyl-octahydro-naphthalen-4a-ol) (1) was investigated by feeding labeled [5,5-2H(2)]-1-desoxy-D-xylulose (11), [4,4,6,6,6-(2)H(5)]-mevalolactone (7) and [2,2-2H(2)]-mevalolactone (9) to Streptomyces sp. JP95 and the liverwort Fossombronia pusilla. The micro-organism produced geosmin via the 1-desoxy-D-xylulose pathway, whereas the liverwort exclusively utilized mevalolactone for terpenoid biosynthesis. Analysis of the labeling pattern in the resulting isotopomers of geosmin (1) by mass spectroscopy (EI/MS) revealed that geosmin is synthesized in both organisms by cyclization of farnesyl diphosphate to a germacradiene-type intermediate 4. Further transformations en route to geosmin (1) involve an oxidative dealkylation of an i-propyl substituent, 1,2-reduction of a resulting conjugated diene, and bicyclization of a germacatriene intermediate 13. The transformations largely resemble the biosynthesis of dehydrogeosmin (2) in cactus flowers but differ with respect to the regioselectivity of the side chain dealkylation and 1,2-reduction

Classification of Terpenoids according to the Methylerythritolphosphate or the Mevalonate Pathway with Natural 12 C/13 C Isotope Ratios: Dynamic Allocation of Resources in Induced Plants.

Plants utilize two different pathways for the biosynthesis of isopentenyl diphosphate, the universal building block of all terpenes. Application of compound-specific isotope-ratio mass spectrometry (GC-C-IRMS) to volatile terpenoids allows distinction between the pathways on the basis of natural 12 C/13 C ratios.