ABSTRACT Weed is one of the major biotic stresses that causes severe loss of crop yield. Herbicide is one of the most cost-effective ways to control weeds. Thus, the development of herbicide-resistant crops is critical for the application of herbicides. To isolate new glufosinate ammonium resistance loci, we screened a rice ethyl methyl sulfonate-mutagenized library and obtained the g lufosinate a mmonium- r esistant mutant gar1-1 . GAR1 encodes auxin response factor 18 ( OsARF18 ). A G-to-A substitution in the coding region of OsARF18 results in loss of function of OsARF18 and thereby enhances glufosinate ammonium resistance of gar1-1 , which was confirmed by three additional CRISPR/Cas9-edited gar1 alleles. GLUTAMINE SYNTHETASE 1;1 ( OsGS1;1 ) and GLUTAMINE SYNTHETASE 1;2 ( OsGS1;2 ) were upregulated in gar1-1 upon glufosinate ammonium treatment, directly contributing to increased GS activity that enhances glufosinate ammonium herbicide resistance. We further show that OsARF18 suppresses OsGS1;1 and OsGS1;2 expression. Comparative transcriptomic analyses reveal a huge shift in the gene expression profile involved in stress tolerance and growth. A large number of detoxification-related genes are enriched in gar1-1 , which may also contribute to enhanced herbicide resistance. Moreover, stress tolerance-related genes are upregulated and growth-related genes are downregulated in gar1-1 , consistent with the improved tolerance to salt and osmotic stress of gar1 mutants. Taken together, our study demonstrates that OsARF18 is a negative regulator of glufosinate ammonium resistance as well as salt and osmotic stress tolerance, suggesting a role in balancing the stress response and growth.

Loss of OsARF18 confers glufosinate ammonium herbicide resistance in rice