Potential sites of bioactive gibberellin production during reproductive growth in Arabidopsis.
Gibberellin 3-oxidase (GA3ox) catalyzes the final step in the synthesis of bioactive gibberellins (GAs). We examined the expression patterns of all four GA3ox genes in Arabidopsis thaliana by promoter-beta-glucuronidase gene fusions and by quantitative RT-PCR and defined their physiological roles by characterizing single, double, and triple mutants. In developing flowers, GA3ox genes are only expressed in stamen filaments, anthers, and flower receptacles. Mutant plants that lack both GA3ox1 and GA3ox3 functions displayed stamen and petal defects, indicating that these two genes are important for GA production in the flower. Our data suggest that de novo synthesis of active GAs is necessary for stamen development in early flowers and that bioactive GAs made in the stamens and/or flower receptacles are transported to petals to promote their growth. In developing siliques, GA3ox1 is mainly expressed in the replums, funiculi, and the silique receptacles, whereas the other GA3ox genes are only expressed in developing seeds. Active GAs appear to be transported from the seed endosperm to the surrounding maternal tissues where they promote growth. The immediate upregulation of GA3ox1 and GA3ox4 after anthesis suggests that pollination and/or fertilization is a prerequisite for de novo GA biosynthesis in fruit, which in turn promotes initial elongation of the silique.
Hu
Jianhong
J
Department of Biology, Duke University, Durham, North Carolina 27708, USA.
Mitchum
Melissa G
MG
Barnaby
Neel
N
Ayele
Belay T
BT
Ogawa
Mikihiro
M
Nam
Edward
E
Lai
Wei-Chu
WC
Hanada
Atsushi
A
Alonso
Jose M
JM
Ecker
Joseph R
JR
Swain
Stephen M
SM
Yamaguchi
Shinjiro
S
Kamiya
Yuji
Y
Sun
Tai-Ping
TP
D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D035264:Flowers / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000096:biosynthesis*; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; D005875:Gibberellins; D006899:Mixed Function Oxygenases; C108186:gibberellin 3beta-hydroxylase