Journal Article

ATHB12, an ABA-Inducible Homeodomain-Leucine Zipper (HD-Zip) Protein of Arabidopsis, Negatively Regulates the Growth of the Inflorescence Stem by Decreasing the Expression of a Gibberellin 20-Oxidase Gene

Ora Son, Yoon-Sun Hur, Yun-Kyung Kim, Hyun-Jung Lee, Sunghan Kim, Mi-Ran Kim, Kyoung Hee Nam, Myung-Sok Lee, Bu-Yong Kim, Jongbum Park, Jungan Park, Suk-Chan Lee, Atsushi Hanada, Shinjiro Yamaguchi, In-Jung Lee, Seoung-Ki Kim, Dae-Jin Yun, Eva Söderman and Choong-Ill Cheon

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 9, pages 1537-1547
Published in print September 2010 | ISSN: 0032-0781
Published online July 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq108
ATHB12, an ABA-Inducible Homeodomain-Leucine Zipper (HD-Zip) Protein of Arabidopsis, Negatively Regulates the Growth of the Inflorescence Stem by Decreasing the Expression of a Gibberellin 20-Oxidase Gene

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Arabidopsis thaliana homeobox 12 (ATHB12) is rapidly induced by ABA and water stress. A T-DNA insertion mutant of ATHB12 with a reduced level of ATHB12 expression in stems had longer inflorescence stems and reduced sensitivity to ABA during germination. A high level of transcripts of gibberellin 20-oxidase 1 (GA20ox1), a key enzyme in the synthesis of gibberellins, was detected in athb12 stems, while transgenic lines overexpressing ATHB12 (A12OX) had a reduced level of GA20ox1 in stems. Consistent with these data, ABA treatment of wild-type plants resulted in decreased GA20ox1 expression whereas ABA treatment of the athb12 mutant gave rise to slightly decreased GA20ox1 expression. Retarded stem growth in 3-week-old A12OX plants was rescued by exogenous GA9, but not by GA12, and less GA9 was detected in A12OX stems than in wild-type stems. These data imply that ATHB12 decreases GA20ox1 expression in stems. On the other hand, the stems of A12OX plants grew rapidly after the first 3 weeks, so that they were almost as high as wild-type plants at about 5 weeks after germination. We also found changes in the stems of transgenic plants overexpressing ATHB12, such as alterations of expression GA20ox and GA3ox genes, and of GA4 levels, which appear to result from feedback regulation. Repression of GA20ox1 by ATHB12 was confirmed by transfection of leaf protoplasts. ABA-treated protoplasts also showed increased ATHB12 expression and reduced GA20ox1 expression. These findings all suggest that ATHB12 negatively regulates the expression of a GA 20-oxidase gene in inflorescence stems.

Keywords: ABA; ATHB12; GA20ox1; Gibberellic acid; Homeobox

Journal Article.  6361 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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