Lolitrems are potent tremorgenic mycotoxins that are synthesised by clavicipitaceous fungal endophytes of the Epichloë/Neotyphodium group in association with grasses. These indole-diterpenes confer major ecological benefits on the grass-endophyte symbiotum. A molecular signature for diterpene biosynthesis is the presence of two geranylgeranyl diphosphate (GGPP) synthases. Using degenerate primers for conserved domains of fungal GGPP synthases, we cloned two such genes, ltmG and ggsA, from Neotyphodium lolii. Adjacent to ltmG are two genes, ltmM and ltmK, that are predicted to encode an FAD-dependent monooxygenase and a cytochrome P450 monooxygenase, respectively. The cluster of ltm genes is flanked by AT-rich retrotransposon DNA that appears to have undergone extensive repeat induced point (RIP) mutation. Epichloë festucae, the sexual ancestor of N. lolii, contains an identical ltm gene cluster, but lacks the retrotransposon "platform'' on the right flank. Associations established between perennial ryegrass and an E. festucae mutant deleted for ltmM lack detectable levels of lolitrems. A wild-type copy of ltmM complemented this phenotype, as did paxM from Penicillium paxilli. Northern hybridization and RT-PCR analysis showed that all three genes are weakly expressed in culture but strongly induced in planta. The relative endophyte biomass in these associations was estimated by real-time PCR to be between 0.3 and 1.9%. Taking this difference into account, the steady-state levels of the ltm transcripts are about 100-fold greater than the levels of the endogenous ryegrass beta-tubulin (beta -Tub1) and actin (Act1) RNAs. Based on these results we propose that ltmG, ltmM and ltmK are members of a set of genes required for lolitrem biosynthesis in E. festucae and N. lolii.

Background: Subtilisin-like proteases (SLPs) form a superfamily of enzymes that act to degrade protein substrates. In fungi, SLPs can play either a general nutritive role, or may play specific roles in cell metabolism, or as pathogenicity or virulence factors.

Lolitrem B is synthesized by Epichloë festucae in associations with Pooid grasses. A complex cluster of at least 10 genes (ltm genes) is required for its synthesis. An early step in this pathway is catalyzed by ltmM, a symbiosis-expressed gene. PltmM-gusA reporter gene analysis was used to monitor ltmM gene expression patterns in planta. The minimum promoter length required for high-level gusA expression in infected seedlings is in the range of 480 to 782 bp. gusA was expressed by the endophyte in all infected vegetative plant tissues and in epiphyllous hyphae. Spikelets from reproductive tillers were analyzed at different developmental stages. During pre-anthesis, gusA expression was observed in all infected floral organs except the immature gynoecium. In post-anthesis florets, gene expression occurred almost exclusively in the gynoecium. Expression of gusA by the endophyte was observed in germinating seeds 24 h postimbibition and seedlings older than 6 days postimbibition in hyphae from the mesocotyl to the tip of the emerging first leaf. This work provides a detailed analysis of the spatial and temporal expression patterns of a symbiosis-expressed gene in planta.

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Although much is known about the beneficial and detrimental effects of the interaction between Neotyphodium lolii and Lolium perenne in the field comparatively little is known about the molecular and cellular events that underlie these effects and how mutualism is maintained. Because N. lolii is quite intractable to genetic analysis we have developed the synthetic association between Epichloë festucae and perennial ryegrass as our model experimental system to study the epichloë endophytegrass symbiotic interaction. Using this system we have recently shown that reactive oxygen species (ROS) produced by a specific endophyte NADPH oxidase (NoxA) have a critical role in regulating hyphal growth and development in perennial ryegrass. We have also shown that two additional components, NoxR and RacA, are required to regulate ROS production to maintain a mutualistic interaction. Using a combined molecular and genetic approach we have recently cloned and characterised genes for peramine and lolitrem biosynthesis. An overview of these advances and the opportunities now available to better understand and exploit this important fungal-grass interaction is presented. Keywords: Epichloë festucae, Neotyphodium lolii, Lolium perenne, peramine, lolitrems, reactive oxygen species