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United States Department of Agriculture

Agricultural Research Service

Research Project: FORAGE SYSTEMS FOR SUSTAINABLE ANIMAL PRODUCTION IN THE MID-SOUTH

Location: Forage-Animal Production Research

Title: Coregulated Expression of Loline Alkaloid-Biosynthesis Genes in Neotyphodium Uncinatum Cultures

Authors
item Zhang, Dong-Xiu -
item Stromberg, Arnold -
item Spiering, Martin -
item Schardl, Christopher -

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2009
Publication Date: April 12, 2009
Citation: Zhang, D., Stromberg, A.J., Spiering, M.J., Schardl, C.L. 2009. Coregulated Expression of Loline Alkaloid-Biosynthesis Genes in Neotyphodium Uncinatum Cultures. Fungal Genetics and Biology. 46:517-530.

Interpretive Summary: 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.

Technical Abstract: 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.

Last Modified: 8/2/2014
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