Isolation and analysis of mutants with altered ABA recognition specificity using an ABA antagonist.

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In order to identify the ABA receptors, we employed a novel screening using an ABA binding inhibitor to isolate mutants that have altered binding specificity of ABA receptors. We used a ABA analogue, PBI-51, as a ABA binding inhibitor since this chemical has been reported to work as ABA binding inhibitor in Brassica napus. We tried to isolate mutants with two type of screening strategies. One is to search for mutants that seem to recognize PB151 as an ABA binding inhibitor. We isolated several candidates from 500,000 M2 seeds from EMS treated plants. However, these candidates turned out to be ABA insensitive mutants. The other strategy was to isolate mutants that seems recognize PB151 as ABA. In this screen, we isolated 8 independent lines from 400,000 M2 seeds from EMS treated plants. Those candidates show ABA-hypersensitivity, although these are not allelic to known ABA-hypersensitive mutants, eral or ein2.To increase the efficiency to isolate ABA receptor mutants, we thought out the strategy to use aba2 mutants, and isolated several dozens of candidates. ldentification of those mutated genes will surely contribute in our understanding on ABA siganling pathway. In the course to isolate ABA related mutants, we isolated a novel ethanol hypersensitiv mutant, gekol, from Arabidopsis. We identified the GEKO I gene by mapping and found it encoded a novel protein that conserved among plants and archea bacteria. GEKO I may play a pivotal role for plant sp ecific functions.