Transcriptomic response in pyroxsulam-resistant and susceptibleBromus sterilisidentified three distinct mechanisms of resistance

Abstract

Bromus sterilis has evolved into a more predominant weed in the Czech Republic's winter wheat fields, owing largely to the widespread application of pyroxsulam for its management. In this study, we report a biotype that has developed resistance to pyroxsulam and has also shown cross-resistance to other herbicides. Although no differences in ploidy levels or no mutations of acetolactate synthase (ALS) were detected, a significant elevation of ALS enzyme activity was observed in the R biotype. Through combined analysis of enzyme inhibition and total transcript expression (RNA-Seq), we have identified differentially expressed transcripts that potentially contribute to pyroxsulam metabolism. Furthermore, we observed a significant increase in the expression of genes involved in redox mechanisms and transporters that could contribute to enhanced resistance to pyroxulam in the R biotype. Our results present a novel understanding of herbicide resistance in B. sterilis through three distinct resistance mechanisms (ALS gene overexpression, enhanced metabolism, and reduced translocation) without mutation in the herbicide target protein. This understanding is the foundation for improving management strategies for herbicide-resistant B. sterilis.