Expression of Two Genes Encoding Gibberellin 2- and 3-oxidases in Developing Seeds of Phaseolus coccineus

;We have isolated PcGA3ox1, a cDNA clone from developing runner bean (Phaseolus coccineus) seeds that shows significant amino acid homology with the gibberellin (GA) 3-oxidases. A recombinant fusion protein of PcGA3ox1 converted GA 20 and GA 9 to GA 1 and GA 4 , respectively. In situ hybridization results showed that transcripts of this gene accumulate specifically within the suspensor of globularstage embryos. PcGA3ox1 mRNA begins to accumulate in the epidermal cells of the embryo proper and is also detectable in the endosperm during the transition from globularto heart-stage embryos. PcGA3ox1 transcripts were localized exclusively in the cotyledons from the early cotyledonary stage up to the cotyledonary stage. Transcripts of the previously cloned GA 2-oxidase (PcGA2ox1) from developing seeds of runner bean were found primarily within the suspensor neck region from the late globular stage up to the heart stage. PcGA2ox1 mRNA was detectable in the whole suspensor from the early cotyledonary stage, and was found in the inner layer of integuments at the cotyledonary stage. Soluble enzyme preparations made from suspensors and embryos at two stages of embryogenesis (the heart and cotyledonary stages) were incubated with [ 14 C]GA20 and [ 14 C]GA 1 . Only young suspensor preparations converted GA 20 to GA 1 and GA 5 . Both suspensor preparations converted GA 1 to GA 8 . Both embryo preparations converted GA20 to GA1, but were unable to convert GA1 to GA8.