Transcriptome profiling to identify cytochrome P450 genes involved in penoxsulam resistance in Echinochloa glabrescens

Cytochrome P450s (P450s) confer resistance against herbicides, and this is increasingly becoming a concern for weed control. As a widespread Gramineae weed in paddy fields, Echinocloa glabrescens has become resistant to the acetolactate synthase (ALS)-inhibiting triazolopyrimidine herbicide penoxsulam. In this study, we found that the GR(50) of the resistant population (SHQP-R) decreased substantially from 25.6 to 5.0 and 6.2 g a.i. ha(-1) after treatment with the P450 inhibitors piperonyl butoxide (PBO) and malathion, respectively. However, P450 inhibitors almost had no effects on the susceptibility of the sensitive population (JYJD-S) to penoxsulam. To investigate the mechanisms of metabolic resistance, transcriptome sequencing analysis was performed to find candidate genes that may confer resistance to penoxsulam in E. glabrescens. A total of 233 P450 differentially expressed genes (DEGs) were identified by transcriptome sequencing. We found that the metabolic process and metabolic pathways were the most highly enriched in DEGs. Further, twenty-seven candidate P450 DEGs were selected for qPCR validation analyses. After penoxsulam treatment, the relative expression levels were significantly higher in SHQP-R than in JYJD-S. Among these, the relative expression of twenty-three P450 DEGs (eighteen from the CYP72A-71C-74A-96A-734A subfamily; five from CYP81E1-94C1-94B3-714C1-714C2) were upregulated and four P450 DEGs (from CYP724B1-711A1-707A7-97B2) were downregulated. Changes in the expression of these candidate P450 genes in E. glabrescens were in response to penoxsulam, which provides preliminary evidence for the role of P450s in herbicide metabolism in E. glabrescens. However, further functional studies on metabolic resistance to penoxsulam in a resistant E. glabrescens population are required.