Chemistry of floral scents in fourLicuala species (Arecaceae)

Caryolan-1-ol, an antifungal volatile produced by Streptomyces spp., inhibits the endomembrane system of fungi

Streptomyces spp. have the ability to produce a wide variety of secondary metabolites that interact with the environment. This study aimed to discover antifungal volatiles from the genus Streptomyces and to determine the mechanisms of inhibition. Volatiles identified from Streptomyces spp. included three major terpenes, geosmin, caryolan-1-ol and an unknown sesquiterpene. antiSMASH and KEGG predicted that the volatile terpene synthase gene clusters occur in the Streptomyces genome. Growth inhibition was observed when fungi were exposed to the volatiles. Biological activity of caryolan-1-ol has previously not been investigated. Fungal growth was inhibited in a dose-dependent manner by a mixture of the main volatiles, caryolan-1-ol and the unknown sesquiterpene, from Streptomyces sp. S4–7. Furthermore, synthesized caryolan-1-ol showed similar antifungal activity. Results of chemical-genomics profiling assays showed that caryolan-1-ol affected the endomembrane system by disrupting sphingolipid synthesis and normal vesicle trafficking in the fungi.

Floral Volatiles in Parasitic Plants of the Orobanchaceae. Ecological and Taxonomic Implications

The holoparasitic broomrapes, Orobanche spp. and Phelipanche spp. (Orobanchaceae), are root parasites that completely depend on a host plant for survival and reproduction. There is considerable controversy on the taxonomy of this biologically and agronomically important family. Flowers of over 25 parasitic Orobanchaceae and a number of close, parasitic and non-parasitic, relatives emitted a complex blend of volatile organic compounds (VOCs), consisting of over 130 VOCs per species. Floral VOC blend-based phylogeny supported the known taxonomy in internal taxonomic grouping of genus and eliminated the uncertainty in some taxonomical groups. Moreover, phylogenetic analysis suggested separation of the broomrapes into two main groups parasitizing annual and perennial hosts, and for the annual hosts, into weedy and non-weedy broomrapes. We conclude that floral VOCs are a significant tool in species identification and possibly even in defining new species and can help to improve controversial taxonomy in the Orobanchaceae.

Twenty-five years of progress in understanding pollination mechanisms in palms (Arecaceae)

BACKGROUND

With more than 90 published studies of pollination mechanisms, the palm family is one of the better studied tropical families of angiosperms. Understanding palm-pollinator interactions has implications for tropical silviculture, agroforestry and horticulture, as well as for our understanding of palm evolution and diversification. We review the rich literature on pollination mechanisms in palms that has appeared since the last review of palm pollination studies was published 25 years ago.

SCOPE AND CONCLUSIONS

Visitors to palm inflorescences are attracted by rewards such as food, shelter and oviposition sites. The interaction between the palm and its visiting fauna represents a trade-off between the services provided by the potential pollinators and the antagonistic activities of other insect visitors. Evidence suggests that beetles constitute the most important group of pollinators in palms, followed by bees and flies. Occasional pollinators include mammals (e.g. bats and marsupials) and even crabs. Comparative studies of palm-pollinator interactions in closely related palm species document transitions in floral morphology, phenology and anatomy correlated with shifts in pollination vectors. Synecological studies show that asynchronous flowering and partitioning of pollinator guilds may be important regulators of gene flow between closely related sympatric taxa and potential drivers of speciation processes. Studies of larger plant-pollinator networks point out the importance of competition for pollinators between palms and other flowering plants and document how the insect communities in tropical forest canopies probably influence the reproductive success of palms. However, published studies have a strong geographical bias towards the South American region and a taxonomic bias towards the tribe Cocoseae. Future studies should try to correct this imbalance to provide a more representative picture of pollination mechanisms and their evolutionary implications across the entire family.

Characterization of a novel sesquiterpene cyclase involved in (+)-caryolan-1-ol biosynthesis in Streptomyces griseus

Most terpenoids have been isolated from plants and fungi and only a few from bacteria. However, an increasing number of genome sequences indicate that bacteria possess a variety of terpenoid cyclase genes. We characterized a sesquiterpene cyclase gene (SGR2079, named gcoA) found in Streptomyces griseus. When expressed in Streptomyces lividans, gcoA directed production of a sesquiterpene, isolated and determined to be (+)-caryolan-1-ol using spectroscopic analyses. (+)-Caryolan-1-ol was also detected in the crude cell lysate of wild-type S. griseus but not in a gcoA knockout mutant, indicating that GcoA is a genuine (+)-caryolan-1-ol synthase. Enzymatic properties were characterized using N-terminally histidine-tagged GcoA, produced in Escherichia coli. As expected, incubation of the recombinant GcoA protein with farnesyl diphosphate yielded (+)-caryolan-1-ol. However, a small amount of another sesquiterpene was also detected. This was identified as the bicyclic sesquiterpene hydrocarbon (+)-β-caryophyllene by comparison with an authentic sample using GC-MS. Incorporation of a deuterium atom into the C-9 methylene of (+)-caryolan-1-ol in an in vitro GcoA reaction in deuterium oxide indicated that (+)-caryolan-1-ol was synthesized by a proton attack on the C-8/C-9 double bond of (+)-β-caryophyllene. Several β-caryophyllene synthases have been identified from plants, but these cannot synthesize caryolan-1-ol. Although caryolan-1-ol has been isolated previously from several plants, the enzyme responsible for its biosynthesis has not been identified previously. GcoA is thus the first known caryolan-1-ol synthase. Isolation of caryolan-1-ol from microorganisms is unprecedented.