Subclass III SnRK2s are essential for ABA responses. (A) Germination test to determine ABA sensitivity in the srk2dei triple mutant. Arabidopsis seeds of Col, srk2dei, abi1–1C, and abi5–7 were sown and grown for 2 weeks on GM agar medium containing 0, 3, or 100 μM ABA. (B) ABA-activated protein kinases in Col, srk2dei, and abi1–1C plants. Three-week-old plants were treated with 50 μM ABA for 0, 30, or 90 min. Upper panel shows in-gel phosphorylation (IGP) assay using histone as a substrate. Black arrow indicates ABA-activated protein kinase (≈40 kDa) overlapping with SnRK2s, and the open arrow indicates the RubisCo large subunit (≈50 kDa) in a CBB-stained gel. The results were confirmed through several replications.