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GENETIC ANALYSIS OF ABA-MEDIATED CONTROL OF PLANT GROWTH IN Arabidopsis
Monika Iten,Thomas Hoffmann,Gregor Benning,Axel Himmelbach,Erwin Grill Plant molecular biology and biotechnology research 1998 Proceedings the 2nd Korean-Germany joint symposium Vol.1998 No.-
The plant hormone abscisic acid (ABA) plays an essential role in a variety of physiological responses such as seed dormancy, regulation of stomatal closure and inhibition of plant growth. We used the inhibitory effect of ABA to isolate mutants of Arabidopsis that reveal ABA-insensitive root growth as a prelude to elucidate the molecular steps of ABA-signalling modulating the growth response of plants. The characterisation of the mutants identified 8 new loci that were subdivided into two classes: pleiotropic mutants including the well-characterised mutants abi1 and abi2 which are impaired in all three above mentioned responses, and mutants that are impaired specifically in the growth response. The cloning of the ABI1 and ABI2 loci and characterisation of its gene products revealed that two homologous protein-serine/threonine phosphatases are components of ABA-signalling. The protein-phosphatases belong to the class 2C and are highly regulated by the pH and magnesium ion concentration. A pH-shift from 7.2 to 7.5 reported to occur in guard cells prior stomatal closure results in a 2.5-fold activation of the protein phosphatase activity. The introduction of a single amino acid exchange in the abi1 as well as in the abi2 protein provides a dominant negative mutation associated with a strongly reduced enzyme activity and a high ABA-insensitivity.