MOLECULAR-GENETICS OF EPICHLOE-TYPHINA AND ACREMONIUM-COENOPHIALUM

The close associations between grasses and endophytes, whereby the fun gi constitute maternally inherited components of the symbiotic entitie s (symbiota), make genetic engineering and other genetic manipulations of the endophytes an attractive approach to improvement of forage, pa sture and turf-grass cultivars. A number of protective alkaloids are p roduced by the endophytes. Although insecticidal, nematocidal and anti microbial metabolites produced by the mycosymbionts are desirable agro nomic characteristics, anti-mammalian activities which are problematic for livestock farmers need to be mitigated. As a necessary prerequisi te for endophyte genetic engineering, the authors have developed a tra nsformation protocol for the tall fescue symbiont Acremonium coenophia lum Morgan-Jones et Gams. The approach used was to introduce the antib iotic resistance gene, hph, which was obtained from the bacterium Esch erichia coli and modified in vitro to allow expression in fungi. Succe ssful incorporation of this 'chimeric' gene into the fungal genome was detected by resistance of the transformants to hygromycin B and by DN A hybridization analysis. The wide variation in the amounts and/or typ es of protective alkaloids produced by different isolates of Epichloe typhina (Fr.) Tulasne (Acremonium typhinum Morgan-Jones et Gams), and other Acremonium spp., raises the prospect of employing the sexual cyc le of E. typhina as an alternative genetic system for development of n ew endophyte strains. However, there is a lack of phenotypically varia ble characters to follow in Mendelian crosses. Therefore, restriction fragment length polymorphisms should be identified and used for geneti c mapping. Preliminary studies of this approach are presented. Genetic manipulations and other approaches to cultivar development based on t he endophytes should be done with an understanding of their evolutiona ry biology and the basis for host preference. Previous studies have ad ded much to the understanding of the alkaloid production potential of different isolates, and the degree of host specificity of both choke p athogens and non-pathogenic endophytes. This paper presents a phylogen etic analysis using DNA sequence information. The results support four conclusions: (1) the endophytes have evolved from E. typhina; (2) the endophytes do not have a strict coevolutionary relationship with thei r grass hosts; (3) loline production, characteristic of certain symbio ta, is not a good indicator of phylogenetic affinities of the fungal s ymbionts; (4) there is a close relationship between isolates of A. coe nophialum from tall fescue, and Acremonium lolii Latch, Samuels et Chr istensen from perennial ryegrass and a non-pathogenic A. typhinum from red fescue.