Herbicide resistance-endowing ACCase gene mutations in hexaploid wild oat (Avena
fatua): insights into resistance evolution in a hexaploid species |
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Authors: | Q Yu M S Ahmad-Hamdani H Han M J Christoffers S B Powles |
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Institution: | 1.Australian Herbicide Resistance Initiative,
School of Plant Biology, Faculty of Natural and Agriculture Sciences, University of
Western Australia, Crawley, Western Australia, Australia;2.Department of Crop Science, Faculty of
Agriculture, Universiti Putra Malaysia, Serdang, Malaysia;3.Department of Plant Sciences, North Dakota
State University, Fargo, ND, USA |
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Abstract: | Many herbicide-resistant weed species are polyploids, but far too little about the
evolution of resistance mutations in polyploids is understood. Hexaploid wild oat
(Avena fatua) is a global crop weed and many populations have evolved herbicide
resistance. We studied plastidic acetyl-coenzyme A carboxylase (ACCase)-inhibiting
herbicide resistance in hexaploid wild oat and revealed that resistant individuals can
express one, two or three different plastidic ACCase gene resistance mutations
(Ile-1781-Leu, Asp-2078-Gly and Cys-2088-Arg). Using ACCase resistance mutations as
molecular markers, combined with genetic, molecular and biochemical approaches, we found
in individual resistant wild-oat plants that (1) up to three unlinked ACCase gene loci
assort independently following Mendelian laws for disomic inheritance, (2) all three of
these homoeologous ACCase genes were transcribed, with each able to carry its own mutation
and (3) in a hexaploid background, each individual ACCase resistance mutation confers
relatively low-level herbicide resistance, in contrast to high-level resistance conferred
by the same mutations in unrelated diploid weed species of the Poaceae (grass) family. Low
resistance conferred by individual ACCase resistance mutations is likely due to a dilution
effect by susceptible ACCase expressed by homoeologs in hexaploid wild oat and/or
differential expression of homoeologous ACCase gene copies. Thus, polyploidy in hexaploid
wild oat may slow resistance evolution. Evidence of coexisting non-target-site resistance
mechanisms among wild-oat populations was also revealed. In all, these results demonstrate
that herbicide resistance and its evolution can be more complex in hexaploid wild oat than
in unrelated diploid grass weeds. Our data provide a starting point for the daunting task
of understanding resistance evolution in polyploids. |
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Keywords: | ACCase mutation Acc1 herbicide resistance hexaploid wild oat (Avena fatua) polyploidy resistance evolution |
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