Rieu I, Eriksson S, Powers SJ, Gong F, Griffiths J, Woodley L, Benlloch R, Nilsson O, Thomas SG, Hedden P, Phillips AL
Genetic analysis reveals that C-19-GA 2 oxidation is a major gibberellin inactivation pathway in Arabidopsis
The Plant Cell: 2008 20(9):2420-2436

Abstract
Bioactive hormone concentrations are regulated both at the levelof hormone synthesis and through controlled inactivation. Basedon the ubiquitous presence of 2β-hydroxylated gibberellins(GAs), a major inactivating pathway for the plant hormone GAseems to be via GA 2-oxidation. In this study, we used variousapproaches to determine the role of C19-GA 2-oxidation in regulatingGA concentration and GA-responsive plant growth and development.We show that Arabidopsis thaliana has five C19-GA 2-oxidases,transcripts for one or more of which are present in all organsand at all stages of development examined. Expression of fourof the five genes is subject to feed-forward regulation. Byknocking out all five Arabidopsis C19-GA 2-oxidases, we showthat C19-GA 2-oxidation limits bioactive GA content and regulatesplant development at various stages during the plant life cycle:C19-GA 2-oxidases prevent seed germination in the absence oflight and cold stimuli, delay the vegetative and floral phasetransitions, limit the number of flowers produced per inflorescence,and suppress elongation of the pistil prior to fertilization.Under GA-limited conditions, further roles are revealed, suchas limiting elongation of the main stem and side shoots. Weconclude that C19-GA 2-oxidation is a major GA inactivationpathway regulating development in Arabidopsis.

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