Neotyphodium

Neotyphodium is a form genus containing species of endophytic fungi. These endophytes are asexual, seed-borne symbionts of cool-season grasses, and grow intercellularly throughout the aerial tissues of their hosts, including shoot apical meristems, leaf sheaths and blades, inflorescences, seeds and embryos.

Taxonomic considerations
Neotyphodium species are closely related to teleomorphic species of the genus Epichloë, from which many have evolved by processes involving interspecific hybridization. . Molecular phylogenetic evidence demonstrates that asexual Neotyphodium species are derived either from individual Epichloë species, or more commonly, from hybrids with at least two ancestral Epichloë species. Hence, the form genus Neotyphodium is very closely associated with the teleomorphic genus Epichloë. In keeping with the code of botanical nomenclature, the form genus refers to the asexual spore or vegetative state, and the teleomorphic genus refers to the sexual state.

Life cycle
The taxonomic dichotomy is especially interesting in this group of symbionts, because vegetative propagation of fungal mycelium occurs by vertical transmission, i.e., fungal growth into newly developing host tillers (=individual grass plants). Importantly, all Neotyphodium and some Epichloëspecies infect new grass plants solely by growing into the seeds of their grass hosts, and infecting the growing seedling. Manifestation of the sexual state - which only occurs in Epichloë fungi — causes choke disease, a condition in which grass inflorescences are engulfed by rapid fungal outgrowth forming a stroma. The fungal stroma suppresses host seed production and culminates in the ejection of meiospores (ascospores) that mediate horizontal (contagious) transmission of the fungus to new plants. .

Effects on the grass plant and on herbivores
It has been proposed that vertically transmitted symbionts should evolve to be mutualists since their reproductive fitness is intimately tied to that of their hosts. In fact, some positive effects of Neotyphodium species on their host plants include increased growth, drought tolerance, and herbivore and pathogen resistance. Resistance against herbivores has been attributed to endophyte-produced alkaloids. Although grass-endophyte symbioses have been widely recognized to be mutualistic in many wild and cultivated grasses, the interactions can be highly variable and sometimes antagonistic, especially under nutrient-poor conditions in the soil.

Neotyphodium alkaloids
Ergoline alkaloids (which are ergot alkaloids, named after the ergot fungus, Claviceps purpurea, a close relative of the Neotyphodium/Epichloë endophytes) are characterized by a ring system derived from 4-prenyl tryptophan. Among the most abundant ergot alkaloids in endophyte-symbiotic grasses is ergovaline, comprising an ergoline moiety attached to a bicyclic tripeptide containing the amino acids, L-proline, L-alanine, and L-valine. Another group of endophyte alkaloids are the indole-diterpenoids, such as lolitrem B. Both the ergoline and indole-diterpenoid alkaloids have biological activity against mammalian herbivores, and also activity against some insects. Peramine is a pyrrolopyrazine alkaloid thought to be biosynthesized from the guanidinium-group-containing amino acid, L-arginine, and pyrrolidine-5-carboxylate, a precursor of L-proline, and is an insect-feeding deterrent. The loline alkaloids are 1-aminopyrrolizidines with an oxygen atom linking bridgehead carbons 2 and 7, and are biosynthesized from the amino acids, L-proline and L-homoserine. The lolines have insecticidal and insect-deterrent activities comparable to nicotine. Many, but not all, Neotyphodium species produce up to three classes of these alkaloids.

Species

 * Neotyphodium aotearoae
 * Neotyphodium australiense
 * Neotyphodium chilense
 * Neotyphodium chisosum
 * Neotyphodium coenophialum
 * Neotyphodium gansuense
 * Neotyphodium huerfanum
 * Neotyphodium lolii
 * Neotyphodium melicicola
 * Neotyphodium occultans
 * Neotyphodium siegelii
 * Neotyphodium starrii
 * Neotyphodium tembladerae
 * Neotyphodium typhinum
 * Neotyphodium uncinatum