Function and transcript analysis of gibberellin-biosynthetic enzymes in wheat.
The enzymes gibberellin (GA) 20-oxidase and 3-oxidase are major sites of regulation in GA biosynthesis. We have characterised one member of each of the gene families encoding these enzymes that are highly expressed in elongating stems and in developing and germinating grains of wheat and are therefore likely to have prominent developmental roles in these tissues. We mapped the three homoeologues of the GA 20-oxidase gene TaGA20ox1 to chromosomes 5BL, 5DL and 4AL. TaGA20ox1 is expressed mainly in the nodes and ears of the elongating stem, and also in developing and germinating embryos. Expression in the nodes, ears and germinating embryos is predominantly from the A and D genomes. Each homoeologous cDNA encodes a functional enzyme that catalyses the multi-step conversions of GA12-GA9, and GA53-GA20. Time course and enzyme kinetic studies indicate that the initial oxidation steps from GA12 and GA53 to the free alcohol forms of GA15 and GA44, respectively, occur rapidly but that subsequent steps occur more slowly. The intermediate GA19 has an especially low affinity for the enzyme, consistent with its accumulation in wheat tissues. The three homoeologous cDNAs for the 3-oxidase gene TaGA3ox2 encode functional enzymes, one of which was shown to possess low levels of 2beta-hydroxylase, 2,3-desaturase, 2,3-epoxidase and even 13-hydroxylase activities in addition to 3beta-hydroxylase activity. In contrast to TaGA20ox1, TaGA3ox2 is expressed in internodes, as well as nodes and the ear of the elongating stem. It is also highly expressed in developing and germinated embryos.
Appleford
Nigel E J
NE
Rothamsted Research, AL5 2JN Harpenden, Herts, UK.
Evans
Daniel J
DJ
Lenton
John R
JR
Gaskin
Paul
P
Croker
Stephen J
SJ
Devos
Katrien M
KM
Phillips
Andrew L
AL
Hedden
Peter
P
D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000302:isolation & purification; D004926:Escherichia coli / Q000235:genetics; D018525:Germination / Q000502:physiology; D005875:Gibberellins / Q000096:biosynthesis*; D007700:Kinetics; D013058:Mass Spectrometry; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018547:Plant Stems / Q000201:enzymology / Q000254:growth & development; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012639:Seeds / Q000201:enzymology / Q000254:growth & development; D014908:Triticum / Q000201:enzymology* / Q000254:growth & development
D018076:DNA, Complementary; D005875:Gibberellins; D010940:Plant Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D006899:Mixed Function Oxygenases; C089210:gibberellin, 2-oxoglutarate-oxygen oxidoreductase (20-hydroxylating, oxidizing)