The Arabidopsis mutant axr1 is defective in both auxin and jasmonic acid responses. A screen for axr1-24 suppressors yielded sar1-5, an allele of previously described mutants that partially correct the auxin response defects in axr1. The new allele partially suppresses defects in jasmonate response in axr1. The JA concentration required for 50% inhibition of seedling root growth was 5-10 mu M for axr1-24 sar1-5. This was at least 10-fold less than that required for axr-24, but 5- to 10-fold higher than for WT. In the axr1-24 background sar1-5 also partially restored resistance to the soil fungus Pythium irregulare, a trait known to require jasmonate signaling. The axr1-24 mutant was equally resistant to JA and JA-Ile, indicating that the defect is not in formation of the JA conjugate that is required for signaling. In contrast to axr1, the tir1-1 mutant that affects the same signaling pathway showed no resistance to jasmonates. Taken together, this evidence argues that the defects in jasmonate response seen in axr1 are not a secondary result of impaired auxin signaling, but that AXR1 functions directly in jasmonate response. Both AXR1 and SAR1 potentially help to coordinate the diverse activities of these 2 important plant signaling pathways.