Gibberellin Is Essentially Required for Carrot (Daucus carotaL.) Somatic Embryogenesis: Dynamic Regulation of Gibberellin 3-Oxidase Gene Expressions

A GA biosynthesis inhibitor, uniconazole, caused many shrunken embryos when it was supplied to cultured carrot (Daucus carota L.) cells at the induction of somatic embryos. The abnormality was prevented by exogenous GA(1) or GA(4). To analyze the status of GA biosynthesis during somatic embryogenesis, expression patterns of newly isolated genes encoding GA biosynthetic enzymes, two GA 20-oxidases, three GA 3-oxidases, and two GA 2-oxidases were observed by using a semi-quantitative reverse-transcription-polymerase chain reaction with gene-specific primers. Transcript levels of GA 20-oxidases and GA 2-oxidases did not change greatly during development of the somatic embryo. On the other hand, drastic changes were found in three GA 3-oxidase genes. Strikingly, expression of a GA 3-oxidase gene, DcGA3ox2, was elevated once in somatic embryogenesis, but not in the non-induced suspension cells. The enzymatic functions of these gene products were also confirmed using recombinant proteins expressed in Escherichia coli. Our results indicate that GA biosynthesis is required for carrot somatic embryogenesis.