Submitted to: Experimental Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/16/2004
Publication Date: 10/5/2004
Citation: Yang, X., Scheffler, B.E., Weston, L.A. 2004. Sor1, a gene associated with bioherbicide production in sorghum root hairs. Experimental Biology. 55(406):2251-2259. Interpretive Summary: Sorghum is allelopathic, meaning it suppresses the growth of neighboring non-sorghum plants. Therefore weed pressure is naturally reduced in sorghum fields. Sorghum root hairs produce large amounts of a compound called sorgoleone which is associated with the allelopathic trait. An experiment was conducted to isolate the genes responsible for sogoleone production. This was done by isolating root hairs and comparing which genes were being expressed in the root hairs to roots with no root hairs. A novel form of a fatty acid desaturase was discovered through this process. Since the chemical structure of sorgoleone has a fatty acid tail, this gene was further characterized. The coding sequence of the gene was characterized as well as its expression pattern. As might be expected, this gene is only expressed in root hairs and not in the other tissues tested.
Technical Abstract: Sorghum [Sorghum bicolor (L.) Moench] roots exude a potent bioherbicide sorgoleone, which is produced in living root hairs and is phytotoxic to broadleaf and grass weeds at concentrations as low as 10 µM. We studied differential gene expression in sorghum (S. bicolor x S. sudanense) cv. SX17 between roots with abundant root hairs and those without root hairs using a modified differential display approach. A differentially expressed gene, named SOR1, was cloned by using Rapid Amplification of 5' Ends of cDNA (5'-RACE). Real-time PCR analysis of multiple tissues of sorghum SX17 revealed that the SOR1 transcript level in root hairs was more than 1,000 times higher than that of other tissues evaluated, including immature leaf, mature leaf, mature stem, panicle, and roots with hairs removed. Semi-quantitative RT-PCR revealed that SOR1 was expressed in the sorgoleone-producing roots of sorghum SX17, shattercane [S. bicolor (L.) Moench], and johnsongrass [S.halepense (L.) Pers.], but not in the shoots of sorghum or in the roots of sweet corn (Zea mays L.) 'Summer Flavor 64Y', in which sorgoleone production was not detected by HPLC analysis. Similarity searches indicated that SOR1 likely encodes for a novel desaturase, which might be involved in the formation of a unique and specific double bonding pattern within the long hydrocarbon tail of sorgoleone.