|Nanyakkara, N.P.D. - UNIVERSITY OF MISSISSIPPI|
Submitted to: American Chemical Society Symposium Series
Publication Type: Book / Chapter
Publication Acceptance Date: January 10, 2005
Publication Date: May 25, 2006
Citation: Baerson, S.R., Dayan, F.E., Rimando, A.M., Pan, Z., Cook, D., Nanyakkara, N., Duke, S.O. A functional genomics approach for the identification of genes involved in the biosynthesis of the allelochemical sorgoleone. Rimando, A.M., Duke, S.O., editors. American Chemical Society, Washington, DC. Natural Products for Pest Management. 2006. p. 265-277. Interpretive Summary: Plant natural products have for many years been viewed as a potential source for new herbicides. Certain species produce compounds referred to as allelochemicals, which inhibit the growth of neighboring susceptible plant species, thus reducing competition for available nutrients and other resources. If the genes are identified which are involved in the production of an allelochemical, it may be possible to use them to develop new plant varieties which are more resistant to weed infestations, and require less herbicides. This report summarizes our efforts to identify the genes involved in producing the allelochemical sorgoleone in sorghum plants. We have generated a database of genes expressed in sorghum root hair cells, where the compound is produced. Using this database, we have identified candidates expressed only in this cell type for all of the genes required to manufacture sorgoleone. We have also provided compelling evidence from biochemistry experiments that one of the methyltransferase DNA sequences in the database does indeed represent one of the enzymes used to produce sorgoleone. The pairing of high throughput cell-specific DNA sequence analysis, and gene expression analysis has proved to be an efficient approach for achieving the technical goals set out for these studies.
Technical Abstract: Several Sorghum species are allelopathic, producing phytotoxins such as sorgoleone and its analogues. Sorgoleone accounts for much of this phytotoxicity, representing up to 90% (w/w) of the content of Sorghum bicolor root exudates. Previous and ongoing studies suggest that the biosynthetic pathway for this compound involves a polyketide synthase activity utilizing atypical long chain fatty acyl-CoA starter units, resulting in the addition of a quinone head via iterative extender unit condensations. An expressed sequence tag (EST) study was performed using random sequences from a Sorghum bicolor root hair-specific cDNA library, and highly expressed candidate sequences representing all of the putative enzyme classes required for the sorgoleone biosynthetic pathway were identified.