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 .