For yew and me

Endophytic fungi live within the tissues of their host plants but, even for fungi, there's no such thing as a free lunch. Some of them pay the rent by producing compounds that protect the host against invading pathogenic microbes. These scanning electron micrographs show three species of endophytic fungus that have mutually beneficial relationships with plants of the family Taxaceae (yews and torreyas). The image at top left shows the highly decorated conidia (asexual spores) of Periconia sp., an endophyte of Torreya grandifolia (from China). This fungus produces taxol — which is toxic to some pathogenic fungi — in an inducible manner. Taxol is also a powerful anti-tumour agent and is one of the most important anti-cancer drugs on the market. The horned conidia of Pestalotiopsis guepinii are shown at top right. This endophyte is found in the stems of the rare Wollemi pines of Australia. Representatives of this fungal genus are the most common producers of taxol worldwide. The doughnut-shaped structure at lower left is the stomatal opening of a European yew leaf, into which the hyphae of the fungus Acremonium sp. are growing. This fungus produces leucinostatins and leucinostatin glucosides — which are active against pathogenic fungi as well as against various leukemia cell lines.