Abstract
BackgroundWater chickweed (Myosoton aquaticum (L.)) is a dicot broadleaf weed that is widespread in winter fields in China, and has evolved serious resistance to acetolactate synthase (ALS) inhibiting herbicides.ResultsWe identified a M. aquaticum population exhibiting moderate (6.15-fold) resistance to tribenuron-methyl (TM). Target-site ALS gene sequencing revealed no known resistance mutations in these plants, and the in vitro ALS activity assays showed no differences in enzyme sensitivity between susceptible and resistant populations; however, resistance was reversed by pretreatment with the cytochrome P450 (CYP) monooxygenase inhibitor malathion. An RNA sequencing transcriptome analysis was performed to identify candidate genes involved in metabolic resistance, and the unigenes obtained by de novo transcriptome assembly were annotated across seven databases. In total, 34 differentially expressed genes selected by digital gene expression analysis were validated by quantitative real-time (qRT)-PCR. Ten consistently overexpressed contigs, including four for CYP, four for ATP-binding cassette (ABC) transporter, and two for peroxidase were further validated by qRT-PCR using additional plants from resistant and susceptible populations. Three CYP genes (with homology to CYP734A1, CYP76C1, and CYP86B1) and one ABC transporter gene (with homology to ABCC10) were highly expressed in all resistant plants.ConclusionThe mechanism of TM resistance in M. aquaticum is controlled by NTSR rather than TSR. Four genes, CYP734A1, CYP76C1, CYP86B1, and ABCC10 could play essential role in metabolic resistance to TM and justify further functional studies. To our knowledge, this is the first large-scale transcriptome analysis of genes associated with NTSR in M. aquaticum using the Illumina platform. Our data provide resource for M. aquaticum biology, and will facilitate the study of herbicide resistance mechanism at the molecular level in this species as well as in other weeds.
Highlights
Water chickweed (Myosoton aquaticum (L.)) is a dicot broadleaf weed that is widespread in winter fields in China, and has evolved serious resistance to acetolactate synthase (ALS) inhibiting herbicides
Treatment with malathion combined with TM increased the sensitivity of the MR population, likely through enhanced metabolism mediated by cytochrome P450 (CYP)
Taking into consideration differences in genetic background and herbicide application in the two populations from different locations, we selected constitutive as well as herbicide-induced genes related to herbicide metabolism that were differentially expressed between MR and S biotypes as candidate genes involved in TM resistance in M. aquaticum
Summary
Water chickweed (Myosoton aquaticum (L.)) is a dicot broadleaf weed that is widespread in winter fields in China, and has evolved serious resistance to acetolactate synthase (ALS) inhibiting herbicides. Herbicide resistance in weeds-which has evolved as an adaptation to herbicide stress-is a global problem threatening crop production. Resistance to herbicides occur via target-site- and non-target site-based resistance mechanisms (TSR and NTSR, respectively). TSR arises from amplification of a target enzyme or structural changes in the herbicide binding site, is widespread in weeds. Acetolactate synthase (ALS)-inhibiting herbicides are applied to a variety of crops worldwide. Their overuse has resulted in the emergence of resistant weeds. At least 160 weed species are currently known to exhibit resistance to ALS inhibitors, which is more than
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