Genetic Evidence in Favor of a Polyketide Origin of Acremeremophilanes, the Fungal "Sesquiterpene" Metabolites.

Eremophilanes are a large group of "sesquiterpenes" produced by plants and fungi, with more than 180 compounds being known in fungi alone. Many of these compounds are phytotoxic, antimicrobial, anticancer and immunomodulators, and hence are of great economic values. Acremeremophilanes A to O have earlier been reported in a marine isolate of Acremonium sp. We report here the presence of Acremeremophilane I, G, K, N, and O, in a plant beneficial fungus Trichoderma virens, in a strain-specific manner. We also describe a novel, P strain-specific polyketide synthase (PKS) gene cluster in T. virens. This gene cluster, designated amm cluster, is absent in the genome of a Q strain of T. virens, and in other Trichoderma spp.; instead, a near identical cluster is present in the genome of the toxic mold Stachybotrys chartarum. Using gene knockout, we provide evidence that acremeremophilanes are biosynthesized via a polyketide route, and not via the mevalonate/terpene synthesis route as believed. We propose here that the 10-carbon skeleton is a product of polyketide synthase, to which a five-carbon isoprene unit is added by a prenyl transferase (PT), a gene for which is present next to the PKS gene in the genome. Based on this evidence, we propose that at least some of the eremophilanes classified in literature as sesquiterpenes (catalyzed by terpene cyclase) are actually meroterpenes (catalyzed by PKSs and PTs), and that the core moiety is not a sesquiterpene, but a hybrid polyketide/isoprene unit. IMPORTANCE The article contradicts the established fact that acremeremophilane metabolites produced by fungi are sesquiterpenes; instead, our findings suggest that at least some of these well-studied metabolites are of polyketide origin. Acremeremophilane metabolites are of medicinal significance, and the present findings have implications for the metabolic engineering of these metabolites and also their overproduction in microbial cell factories.

Characterization of the olfactory system of the giant honey bee, Apis dorsata.

Apis dorsata is an open-nesting, undomesticated, giant honey bee found in southern Asia. We characterized a number of aspects of olfactory system of Apis dorsata and compared it with the well-characterized, western honeybee, Apis mellifera, a domesticated, cavity-nesting species. A. dorsata differs from A. mellifera in nesting behavior, foraging activity, and defense mechanisms. Hence, there can be different demands on its olfactory system. We elucidated the glomerular organization of A. dorsata by creating a digital atlas for the antennal lobe and visualized the antennal lobe tracts and localized their innervations. We showed that the neurites of Kenyon cells with cell bodies located in a neighborhood in calyx retain their relative neighborhoods in the pedunculus and the vertical lobe forming a columnar organization in the mushroom body. The vertical lobe and the calyx of the mushroom body were found to be innervated by extrinsic neurons with cell bodies in the lateral protocerebrum. We found that the species was amenable to olfactory conditioning and showed good learning and memory retention at 24 h after training. It was also amenable to massed and spaced conditioning and could distinguish trained odor from an untrained novel odor. We found that all the above mentioned features in A. dorsata are very similar to those in A. mellifera. We thereby establish A. dorsata as a good model system, strikingly similar to A. mellifera despite the differences in their nesting and foraging behavior.

Effect of heavy metals on germination of seeds.

With the expansion of the world population, the environmental pollution and toxicity by chemicals raises concern. Rapid industrialization and urbanization processes has led to the incorporation of pollutants such as pesticides, petroleum products, acids and heavy metals in the natural resources like soil, water and air thus degrading not only the quality of the environment, but also affecting both plants and animals. Heavy metals including lead, nickel, cadmium, copper, cobalt, chromium and mercury are important environmental pollutants that cause toxic effects to plants; thus, lessening productivity and posing dangerous threats to the agro-ecosystems. They act as stress to plants and affect the plant physiology. In this review, we have summarized the effects of heavy metals on seeds of different plants affecting the germination process. Although reports exist on mechanisms by which the heavy metals act as stress and how plants have learnt to overcome, the future scope of this review remains in excavating the signaling mechanisms in germinating seeds in response to heavy metal stress.