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Hydrogen peroxide (H2O2) is a reactive oxygen species that affects cell signaling in various plant defense responses and induces programmed cell death.To identify the new components associated with H2O2 signaling and tolerance,we conducted a genome-wide association study (GWAS) on the root growth of 133 Arabidopsis thaliana accessions grown in the presence of toxic H2O2 levels.The most significant SNPs were associated with a cluster of chromosome 4 genes encoding an aquaporin NODULIN 26-LIKE INTRINSIC PROTEIN 1;1 (NIP1;1),an NB-ARC domain-containing disease resistance protein (AT4G19050),and a putative membrane lipoprotein (AT4G19070).The expression level of NIP1;1 was relatively high in A.thaliana accessions sensitive to H2O2.Additionally,overexpression of NIP1;1 in a tolerant accession (e.g.,Col-0) increased the sensitivity of transgenic plants to H2O2.An in planta β-glucuronidase reporter assay revealed that variations in the NIP1;1 promoter were responsible for the differences of its expression level in H2O2-tolerant and-sensitive accessions.Cell death was extensive and H2O2 levels were high in the roots of H2O2-sensitive and NIP1;1-overexpressing accessions.Together,our results indicate that the aquaporin NIP1;1 is a key determinant of the sensitivity ofA.thaliana to H2O2,and contributes to the phenotypic variations detected by our GWAS.