Arabidopsis IQMs share sequence homology with a pea heavy metal-induced protein 6 and a trichosanthin.Distinct expression patterns for each gene suggest that each IQM family member may play a different role in plant development and response to environmental cues.However functions of the IQM family members remain to be analyzed.IQM1 can bind with AtCaM5 in yeast two-hybrid assay via its IQ-motif.The CaM binding was Ca2+-independent in vitro, and was also observed in bimolecular fluorescence complementation analyses in onion epidermal cells.IQM1 was found to express strongly in guard cells and the cortex of roots.The T-DNA insertion mutants of IQM1 (iqm1) displayed a smaller stomatal aperture, a decreased water loss rate and a shorter primary root.Moreover, iqm1 did not change its stomatal aperture when treated with light, dark, ABA and chitin obviously.Stomatal guard cell of iqm1-1 also showed enhanced expression of genes involved in production and signaling of reactive oxygen species (ROS).Consistently, increased ROS level was observed in guard cells.Interestingly, 243 and 28 genes were up-and down-regulated by more than two fold in the leaf of iqm1-1, respectively.Particularly, 34 of 117 and 7 of 30 chitin-responsive transcriptional factor and ubiquitin ligase genes were up-regulated.Furthermore 51 defense-associated genes in iqm1-1 were also up-regulated.Consistent with above, iqm1-1 was found to be more resistant to Pst DC3000 than wild type when the pathogen is sprayed, but to show similar symptom to wild type when the pathogen is infiltrated, suggesting that IQM1 is involved in stomatal innate immune.Our further results showed that mutation ofIQM1 reduces sensitivity to JA which enhances stomatal aperture and consequently reduces resistance to Pst DC3000, indicating that IQM1 enhance JA signal transduction and stomatal open and consequently reduce resistance to Pst DC3000.