Wei Li,Lele Zhang,Ning Zhao,Wenlei Guo,Weitang Liu,Lingxu Li,Jinxin Wang
ABSTRACT American slough grass ( Beckmannia syzigachne (Steud.( Fernald) is a worldwide weed and is widely distributed in rice-wheat rotations in China. Fenoxaprop- P -ethyl and mesosulfuron-methyl are two major herbicides used to control B. syzigachne . Resistance has evolved in B. syzigachne under continuous selective pressure from herbicides. This study aimed to establish the cross-resistance pattern of a resistant population and explore the potential non-target-site based resistance mechanisms of B. syzigachne . Sequencing of target enzyme genes (acetyl coenzyme A carboxylase (ACCase( and acetolactate synthase (ALS() revealed that there were no resistance-endowing amino acid substitutions in the resistant B. syzigachne population (R F1 ) compared with the sensitive population (S F1 ), and obtained the purified materials. Furthermore, piperonyl butoxide (PBO) and malathion showed synergistic effects with fenoxaprop- P -ethyl and mesosulfuron-methyl respectively in R F1 . Therefore, we speculate that the resistance observed in B. syzigachne was related with metabolic, mostly involving the cytochrome P450 enzymes. Cross resistance patterns showed that the purified resistant B. syzigachne produce high resistance to fenoxaprop- P -ethyl and pyroxsulam; intermediate resistance to flucarbazone-sodium; low resistance to quizalofop- P -ethyl, clodinafop-propargyl, sethoxydim and mesosulfuron-methyl; sensitive to clethodim pinoxaden and isoproturon. Key words: Herbicide resistance; metabolic resistance; P450 inhibitors; target enzymes sequencing.
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.
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