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.
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 GA(9), but not by GA(12), and less GA(9) 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 GA(4) 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.
Son
Ora
O
Department of Biological Science, Sookmyung Women's University, Seoul 140-742, Korea.
Hur
Yoon-Sun
YS
Kim
Yun-Kyung
YK
Lee
Hyun-Jung
HJ
Kim
Sunghan
S
Kim
Mi-Ran
MR
Nam
Kyoung Hee
KH
Lee
Myung-Sok
MS
Kim
Bu-Yong
BY
Park
Jongbum
J
Park
Jungan
J
Lee
Suk-Chan
SC
Hanada
Atsushi
A
Yamaguchi
Shinjiro
S
Lee
In-Jung
IJ
Kim
Seoung-Ki
SK
Yun
Dae-Jin
DJ
Söderman
Eva
E
Cheon
Choong-Ill
CI
D000040:Abscisic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D056626:Inflorescence / Q000254:growth & development*; D016350:Leucine Zippers; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D018547:Plant Stems / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological
D029681:Arabidopsis Proteins; D005875:Gibberellins; D018398:Homeodomain Proteins; D000040:Abscisic Acid; D006899:Mixed Function Oxygenases; C089210:gibberellin, 2-oxoglutarate-oxygen oxidoreductase (20-hydroxylating, oxidizing)