Target-site basis for resistance to imazethapyr in redroot amaranth (Amaranthus retroflexus L.)

• Dose–response tests showed one redroot amaranth population was resistant to imazethapyr.
• ALS activity assay showed the imazethapyr I50 value for R was much higher than that for S.
• Sequences analysis revealed an Asp-376-Glu substitution in ALS in R population.
• Asp-376-Glu was first found in redroot amaranth.

Experiments were conducted to confirm imazethapyr resistance in redroot amaranth (Amaranthus retroflexus L.) and study the target-site based mechanism for the resistance. Whole-plant response experiments revealed that the resistant (R) population exhibited 19.16 fold resistance to imazethapyr compared with the susceptible (S) population. In vitro ALS activity assay demonstrated that the imazethapyr I50 value of the R population was 21.33 times greater than that of the S population. However, qRT-PCR analysis revealed that there is no difference in ALS gene expression between the R and S populations. Sequence analysis revealed an Asp-376-Glu substitution in ALS in the R population. In order to verify that the imazethapyr resistance was conferred by Asp-376-Glu mutation, the ALS-R and ALS-S genes were fused to the CaMV 35S promoter and introduced into Arabidopsis respectively. The expression of ALS-R in transgenic Arabidopsis plants exhibited 13.79 fold resistance to imazethapyr compared to ALS-S transgenic Arabidopsis.

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