Molecular and genetic methodologies and transformation of grass endophytes

The Acremonium endophytes — those fungi with a close phylogenetic relationship to the ascomycetous genus Epichloê (Clavicipitaceae) — have a remarkable life cycle that, though perhaps not unique, is nevertheless unusual among plant-biotrophic fungi. Many species of Epichloê and Acremonium endophytes (see Chapter 1) are capable of clonal dissemination via endophytic infection of host seeds, during which they neither produce external spores nor cause demonstrable disease on their hosts. 5 The extreme circumstance typifies the symbionts that I will refer to as endophytes sensu stricto, which have never been known to produce infectious spores in nature and, apparently, rely entirely on seed transmission. Because of this life cycle, they are confined to host matrilines in much the same way as are cellular organelles (e.g., mitochondria and plastids). However, they differ from organelles in that the endophytes grow intercellularly, rather than intracellularly, and are not required for basic life processes of their host grasses. The dependence of a host on an endophyte is ecological, being based on the profound enhancement of stress tolerance, that the endophyte can confer on its host.