| Summary: | Barnyardgrass (<i>Echinochloa crus-galli</i> L.) is the most serious weed threatening rice production, and its effects are aggravated by resistance to the quinclorac herbicide in the Chinese rice fields. This study conducted a comparative proteomic characterization of the quinclorac-treated and non-treated resistant and susceptible <i>E. crus-galli</i> using isobaric tags for relative and absolute quantification (iTRAQ). The results indicated that the quinclorac-resistant <i>E. crus-galli</i> had weaker photosynthesis and a weaker capacity to mitigate abiotic stress, which suggested its lower environmental adaptability. Quinclorac treatment significantly increased the number and expression of the photosynthesis-related proteins in the resistant <i>E. crus-galli</i> and elevated its photosynthetic parameters, indicating a higher photosynthetic rate compared to those of the susceptible <i>E. crus-galli</i>. The improved adaptability of the resistant <i>E. crus-galli</i> to quinclorac stress could be attributed to the observed up-regulated expression of eight herbicide resistance-related proteins and the down-regulation of two proteins associated with abscisic acid biosynthesis. In addition, high photosynthetic parameters and low glutathione thiotransferase (GST) activity were observed in the quinclorac-resistant <i>E. crus-galli</i> compared with the susceptible biotype, which was consistent with the proteomic sequencing results. Overall, this study demonstrated that the resistant <i>E. crus-galli</i> enhanced its adaptability to quinclorac by improving the photosynthetic efficiency and GST activity.
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