The acetolactate synthase (ALS) inhibitor mesosulfuron-methyl is currently the only selective herbicide to control Aegilops tauschii in wheat fields; however, the mechanism underlying this selectivity remains unclear. Results showed that the tolerance of Triticum aestivum to mesosulfuron-methyl was much higher than that of A. tauschii. Mesosulfuron-methyl inhibited the in vitro ALS activity of A. tauschii and T. aestivum similarly, but the predicted structural interactions of ALS with mesosulfuron-methyl and induced expression of als were different in the two species. Compared with T. aestivum, A. tauschii was found to absorb more mesosulfuron-methyl and metabolize much less mesosulfuron-methyl. The cytochrome P450 monooxygenase (CYP450) inhibitor, malathion, greatly increased the sensitivity of T. aestivum to mesosulfuron-methyl, while its synergistic effect was smaller in A. tauschii. Finally, 19 P450 genes were selected as candidate genes related with metabolism-based mesosulfuron-methyl selectivity. Collectively, different sensitivities to mesosulfuron-methyl in the two species were likely to be attributed to metabolism variances.

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