Genome sequence of aod6 mutant derived from Arabidopsis thaliana Bu-5

We previously found that a salt-tolerant Arabidopsis accession containing Bu-5 showed osmotic tolerance after salt acclimation, while the experimental accession Col-0 did not. We isolated a Bu-5 background mutant, acquired osmotolerance-defective 6 (aod6), impairing in not only acquired osmotolerance but also osmo-shock, salt-shock and oxidative stress-tolerances with a smaller plant size compared to WT. We found that AOD6 encodes CATION/CALCIUM EXCHANGER 4 (CCX4). The aod6 mutant was more sensitive to both Ca2+ deficiency and high Ca2+ concentration than the wild type (WT). In addition, aod6 accumulates higher Ca2+ in the shoots than WT, suggesting that Ca2+ homeostasis is disturbed in aod6. We also found that aod6 enhanced MPK3/6-mediated immune responses under osmotic stress.