Epichloë endophytes (holomorphic Epichloë spp. and anamorphic Neotyphodium spp.) are systemic, often heritable symbionts of cool-season grasses (subfamily Pooideae). Many epichloae provide protection to their hosts by producing anti-insect compounds. Among these are the loline alkaloids (LA), which are toxic and deterrent to a broad range of herbivorous insects but not to mammalian herbivores. LOL, a gene cluster containing nine genes, is associated with LA biosynthesis. We investigated coordinate regulation between LOL-gene expression and LA production in minimal medium (MM) cultures of Neotyphodium uncinatum. Expression of all LOL genes significantly fit temporal quadratic patterns during LA production. LOL-gene expression started before LA were detectable, and increased while LA accumulated. The highest gene expression level was reached at close to the time of most rapid LA accumulation, and gene expression declined to a very low level as amounts of LA plateaued. Temporal expression profiles of the nine LOL genes were tightly correlated with each other, but not as tightly correlated with proC and metE (genes for biosynthesis of precursor amino acids). Furthermore, the start days and peak days of expression significantly correlated with the order of the LOL-cluster genes in the genome. Hierarchical cluster analysis indicated three pairs of genes-lolA and lolC, lolO and lolD, and lolT and lolE-expression of which was especially tightly correlated. Of these, lolA and lolC tended to be expressed early, and lolT and lolE tended to be expressed late, in keeping with the putative roles of the respective gene products in the LA-biosynthesis pathway. Several common transcriptional binding sites were discovered in the LOL upstream regions. However, low expression of PlolC2uidA and PlolA2uidA in N. uncinatum transformants suggested induced expression of LOL genes might be subject to position effect at the LOL locus.
|Number of pages||14|
|Journal||Fungal Genetics and Biology|
|State||Published - Aug 2009|
Bibliographical noteFunding Information:
This work was supported by US Department of Agriculture CSREES grants 200506271031 and 200710021743. The E. festucae genome and cDNA sequences were determined with support of NSF Grant EF-0523661 and US Department of Agriculture National Research Initiative Grant 20053531916141. We thank Walter Hollin and Emily Gay for valuable technical support, and Uljana Hesse for providing assembled genomic and cDNA sequences. This is Kentucky Agricultural Experiment Station publication number 09-12-026 published with the approval of the director.
- Gene cluster
- Gene expression
- Grass endophytes
- Loline alkaloids
- Neotyphodium uncinatum
ASJC Scopus subject areas