Pro-197-Ser Mutation in ALS and High-Level GST Activities: Multiple Resistance to ALS and ACCase Inhibitors in Beckmannia syzigachne.

Jingjing Wang,Dan Li,Xiangju Li,Zheng Li,Hailan Cui,Jingchao Chen

doi:10.3389/fpls.2020.572610

Abstract

American sloughgrass (Beckmannia syzigachne Steud.) is one of the most troublesome weeds infesting wheat and canola fields in China. Some biotypes cannot be controlled, either by acetolactate synthase (ALS) or acetyl coenzyme A carboxylase (ACCase) inhibitors, which are the main herbicides for controlling this weed. However, very few studies have investigated multiple resistance mechanism in B. syzigachne. In this study, a B. syzigachne biotype with a high resistance to ALS inhibitors we have reported was also showed relatively lower resistance to ACCase inhibitors, with a resistance index around 7. RNA-seq analysis was used to investigate the factors responsible for multiple resistance, and 60,108 unigenes were assembled by de novo transcriptome assembly and then annotated across eight databases. A Pro-197-Ser mutation was identified in the ALS gene by SNPs analysis and validated by PCR, while no mutation was identified in the ACCase gene. Nineteen candidate metabolic genes were screened and their overexpression was confirmed by qPCR. The expression of GST-T3 and GST-U6 in resistant plants ranged from 7.5- to 109.4-folds than that in susceptible ones at different times after two kinds of herbicide treatment. In addition, GST activities in resistant plants were 3.0–5.0 times higher than that in susceptible plants. Other novel resistance factors also showed high correlation with multiple resistance which included four genes encoding disease resistance proteins, a transcription factor (MYC3), and one gene conferring blight resistance. In this research, a B. syzigachne biotype was confirmed to have evolved multiple resistance to ACCase and ALS inhibitors. The Pro-197-Ser mutation in ALS gene and high-level GST activities were confirmed responsible for the multiple resistance. Characterized disease-resistance proteins, transcription factor, and blight-resistance proteins may play an essential role in these multiple herbicide resistance.

Highlights

American sloughgrass (Beckmannia syzigachne Steud.) is a troublesome diploid weed (2n = 14), which threatens many crop varieties in China such as wheat (Triticum aestivum L.) and oilseed rape [Brassica rapa L. subsp
For the R biotype WC1148, the GR50 values were 87.0, 39.4, 84.5, and 89.2 g a. i. ha-1, respectively. Compared with those of the sensitive biotypes, the resistance index (RI) of WC1148 were 2.1, 3.3, 7.4 and 7.5, respectively (Table 1). These results indicated that the acetolactate synthase (ALS) inhibitors resistant biotype WC1148 evolved multiple resistance to the acetyl coenzyme A carboxylase (ACCase) inhibitors
The results show that expression of these two genes in the R individuals was higher than that in the S individuals at each time point under herbicide treatment (Figure 4)

Summary

Introduction

American sloughgrass (Beckmannia syzigachne Steud.) is a troublesome diploid weed (2n = 14), which threatens many crop varieties in China such as wheat (Triticum aestivum L.) and oilseed rape [Brassica rapa L. subsp. Inhibitors of acetyl coenzyme A carboxylase (ACCase; EC 6.4.1.2) and acetolactate synthase (ALS; EC 4.1.3.18) are the main herbicides that are used to control the B. syzigachne in China. After many years of selection pressure, this weed evolved cross- or multiple-resistance to these two mechanisms of herbicides (Li et al, 2013; Li et al, 2015; Li et al, 2017). Resistant B. syzigachne can survive under high doses of these two kinds of herbicides via a variety of mechanisms. We sought to investigate resistance mechanisms useful for its control

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