KNOX homeodomain protein directly suppresses the expression of a gibberellin biosynthetic gene in the tobacco shoot apical meristem.
To identify genes targeted by the tobacco KNOX homeodomain protein, Nicotiana tabacum homeobox 15 (NTH15), we have generated an inducible system using the human glucocorticoid receptor. In this system, steroid treatment strictly induced NTH15 function and immediately suppressed the expression of a gibberellin (GA) biosynthetic gene encoding GA 20-oxidase (Ntc12) and also resulted in a decrease in bioactive GA levels. The repression of Ntc12 was observed even when indirect effects were blocked by cycloheximide. NTH15 mRNA was present in corpus cells of the shoot apical meristem (SAM), whereas Ntc12 mRNA was observed in leaf primordia and rib meristem but not in the corpus. Recombinant NTH15 protein strongly bound to a 5-bp dyadsymmetric sequence, GTGAC, in the first intron of Ntc12 in vitro. Mutation of this sequence in the Ntc12 gene abolished the NTH15-dependent suppression of Ntc12 in the corpus of the SAM. Our results indicate that NTH15 directly represses Ntc12 expression in the corpus of the wild-type SAM to maintain the indeterminate state of corpus cells. The suppression of NTH15 within cells at the flanks of the SAM permits GA biosynthesis, which promotes organized cell proliferation and consequently induces the determination of cell fate.
Sakamoto
T
T
Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
Kamiya
N
N
Ueguchi-Tanaka
M
M
Iwahori
S
S
Matsuoka
M
M
D002455:Cell Division; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000096:biosynthesis / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D017403:In Situ Hybridization; D007438:Introns; D018519:Meristem / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000235:genetics* / Q000378:metabolism
D005875:Gibberellins; D018398:Homeodomain Proteins; C095848:Kn1 protein, plant; C109677:NTH15 protein, Nicotiana tabacum; D010940:Plant Proteins; D011965:Receptors, Glucocorticoid; D011993:Recombinant Fusion Proteins; D006899:Mixed Function Oxygenases; C089210:gibberellin, 2-oxoglutarate-oxygen oxidoreductase (20-hydroxylating, oxidizing)