BACKGROUND: Target-site resistance is the major cause of herbicide resistance to acetolactate synthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides in arable weeds, whereas non-target-site resistance is rarely reported. In the Echinochloa phyllopogon biotypes resistant to these herbicides, target-site resistance has not been reported, and non-target-site resistance is assumed to be the basis for resistance. To explore why target-site resistance had not occurred, the target-site genes for these herbicides were isolated from E. phyllopogon, and their expression levels in a resistant biotype were determined. RESULTS: Two complete ALS genes and the carboxyltransferase domain of four ACCase genes were isolated. The expression levels of ALS and ACCase genes were higher in organs containing metabolically active meristems, except for ACC4, which was not expressed in any organ. The differential expression among examined organs was more prominent for ALS2 and ACC2 and less evident for ALS1, ACC1 and ACC3. CONCLUSION: E. phyllopogon has multiple copies of the ALS and ACCase genes, and different expression patterns were observed among the copies. The existence of three active ACCase genes and the difference in their relative expression levels could influence the occurrence of target-site resistance to ACCase inhibitors in E. phyllopogon.
BACKGROUND: Target-site resistance is the major cause of herbicide resistance to acetolactate synthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides in arable weeds, whereas non-target-site resistance is rarely reported. In the Echinochloa phyllopogon biotypes resistant to these herbicides, target-site resistance has not been reported, and non-target-site resistance is assumed to be the basis for resistance. To explore why target-site resistance had not occurred, the target-site genes for these herbicides were isolated from E. phyllopogon, and their expression levels in a resistant biotype were determined. RESULTS: Two complete ALS genes and the carboxyltransferase domain of four ACCase genes were isolated. The expression levels of ALS and ACCase genes were higher in organs containing metabolically active meristems, except for ACC4, which was not expressed in any organ. The differential expression among examined organs was more prominent for ALS2 and ACC2 and less evident for ALS1, ACC1 and ACC3. CONCLUSION:E. phyllopogon has multiple copies of the ALS and ACCase genes, and different expression patterns were observed among the copies. The existence of three active ACCase genes and the difference in their relative expression levels could influence the occurrence of target-site resistance to ACCase inhibitors in E. phyllopogon.