title: RNA-Seq transcriptome analysis to identify genes involved in metabolism-based diclofop resistance in Lolium rigidum.
abstract: Weed control failures due to herbicide resistance are an increasing and worldwide problem that significantly affect crop yields. Metabolism-based herbicide resistance (referred to as metabolic resistance) in weeds is not well characterized at the genetic level. An RNA-Seq transcriptome analysis was used to find candidate genes that conferred metabolic resistance to the herbicide diclofop in a diclofop-resistant population (R) of the major global weed Lolium rigidum. A reference cDNA transcriptome (19 623 contigs) was assembled and assigned putative annotations. Global gene expression was measured using Illumina reads from untreated control, adjuvant-only control, and diclofop treatment of R and susceptible (S). Contigs that showed constitutive expression differences between untreated R and untreated S were selected for further validation analysis, including 11 contigs putatively annotated as cytochrome P450 (CytP450), glutathione transferase (GST), or glucosyltransferase (GT), and 17 additional contigs with annotations related to metabolism or signal transduction. In a forward genetics validation experiment, nine contigs had constitutive up-regulation in R individuals from a segregating F2 population, including three CytP450, one nitronate monooxygenase (NMO), three GST, and one GT. Principal component analysis using these nine contigs differentiated F2 -R from F2 -S individuals. In a physiological validation experiment in which 2,4-D pre-treatment induced diclofop protection in S individuals due to increased metabolism, seven of the nine genetically validated contigs were induced significantly. Four contigs (two CytP450, NMO, and GT) were consistently highly expressed in nine field-evolved metabolic resistant L. rigidum populations. These four contigs were strongly associated with the resistance phenotype and are major candidates for contributing to metabolic diclofop resistance.
authors.affiliation: Australian Herbicide Resistance Initiative (AHRI), School of Plant Biology, University of Western Australia, Crawley, 6009, Western Australia, Australia; Bayer CropScience, Weed Resistance Research, 65926, Frankfurt am Main, Germany.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Gaines
authors.forename: Lothar
authors.initials: L
authors.lastname: Lorentz
authors.forename: Andrea
authors.initials: A
authors.lastname: Figge
authors.forename: Johannes
authors.initials: J
authors.lastname: Herrmann
authors.forename: Frank
authors.initials: F
authors.lastname: Maiwald
authors.forename: Mark-Christoph
authors.initials: MC
authors.lastname: Ott
authors.forename: Heping
authors.initials: H
authors.lastname: Han
authors.forename: Roberto
authors.initials: R
authors.lastname: Busi
authors.forename: Qin
authors.initials: Q
authors.lastname: Yu
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Powles
authors.forename: Roland
authors.initials: R
authors.lastname: Beffa
mesh_terms: D055768:Halogenated Diphenyl Ethers / Q000633:toxicity; D053209:Herbicide Resistance / Q000235:genetics / Q000502:physiology; D008129:Lolium / Q000187:drug effects* / Q000378:metabolism*; D059467:Transcriptome / Q000235:genetics
chemical_list: D055768:Halogenated Diphenyl Ethers; C012891:dichlorfop-methyl
keywords: Lolium rigidum; diclofop-methyl; herbicide metabolism; herbicide resistance; next-generation sequencing; transcriptional markers; transcriptomics