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Title: Ethylmethanesulfonate Saturation Mutagenesis in Arabidopsis to Determine Frequency of Herbicide Resistance

item Baerson, Scott

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2002
Publication Date: 1/1/2003
Citation: Jander, G., Baerson, S.R., Hudak, J.A., Gonzalez, K.A., Gruys, K.J., Last, R.L. 2003. Ethylmethanesulfonate Saturation Mutagenesis in Arabidopsis to Determine Frequency of Herbicide Resistance. Plant Physiology. 131:139-146.

Interpretive Summary: The occurrence of spontaneous resistance to the herbicide glyphosate has been generally less frequent than for other herbicides, however this supposition has never been tested under controlled experimental conditions. We therefore used three mutagenized populations of the experimental model plant Arabidopsis grown in parallel and treated them with either the herbicide glyphosate, chlorsulfuron, or imazethapyr. Consistent with field reports, no glyphosate resistant individuals were observed, however individuals resistant to chlorsulfuron and imazethapyr were recovered at a significant rate. In addition, the target gene, acetolactate synthase, was sequenced in the imazethapyr resistant individuals obtained in the screen, and two previously unreported mutations capable of conferring resistance to this herbicide were identified.

Technical Abstract: Plant resistance to glyphosate has been reported far less frequently than resistance to sulfonylurea and imidazolinone herbicides. However, these studies tend to be anecdotal, without side by side comparisons for a single species or natural isolate. In this study, we tested the frequencies of resistance of three herbicides in a controlled ethylmethanesulfonate (EMS) saturation mutagenesis experiment, allowing a direct comparison of the frequencies at which resistant mutant plants arise. The 100% growth inhibition dose rates of glyphosate, chlorsulfuron (a sulfonylurea herbicide), and imazethapyr (an imidazolinone herbicide) were determined for Arabidopsis. Populations of EMS-mutagenized M2 seedlings were sprayed with twice the 100% growth inhibition dose of glyphosate, chlorsulfuron, or imazethapyr, and herbicide-resistant mutants were identified. Although there were no glyphosate-resistant mutants among M2 progeny of 125,000 Columbia and 125,000 Landsberg erecta M1 lines, chlorsulfuron resistance and imazethapyr resistance each appeared at frequencies of 3.2 10[1]5. Given the observed frequency of herbicide resistance mutations, we calculate that there are at least 700 mutations in each EMS-mutagenized Arabidopsis line and that fewer than 50,000 M1 lines are needed to have a 95% chance of finding a mutation in any given G:C base pair in the genome. As part of this study, two previously unreported Arabidopsis mutations conferring resistance to imidazolinone herbicides, csr1-5 (Ala-122-Thr) and csr1-6 (Ala-205-Val), were discovered. Neither of these mutations caused enhanced resistance to chlorsulfuron in Arabidopsis.