ISHS Acta Horticulturae 463: VIII International Symposium on Plant Bioregulation in Fruit Production
A RICE HOMEOBOX GENE, OSH1, ALTERS MORPHOLOGY OF KIWIFRUIT AND INHIBITS THE GIBBELLIN BIOSYNTHESIS |
| Authors: | S. Kusaba, Y. Kano-Murakami, T. Sakamoto, M. Matsuoka, N. Matsuta, I. Yamaguchi, M. Fukumoto |
| Keywords: | Morphogenesis, transformation, ELISA, dwarf |
| Abstract:
The rice gene, OSH1, has the homeobox sequence which is conserved among homeotic genes in Drosophila, and its gene product is thought to have DNA binding activity. We introduced an OSH1 cDNA into kiwifruit plants to elucidate the mechanism(s) of morphogenesis in fruit tree. The morphology of transgenic kiwifruits could be divided into three categories, normal-, mild- and severe-phenotype. We performed RNA blot analysis to investigate the gene expression dose-dependence of the morphological changes in kiwifruit. Severe-phenotype plants showed the highest level of OSH1 expression of all transgenic and wild type kiwifruit plants. Only a small amount of OSH1 transcript was observed in some transgenic kiwifruits that caused no morphological change. These results indicate that severity of morphological changes in OSH1-transformed kiwifruit plants depends on the expression level of OSH1. The transformants with severe-phenotype are extremely dwarf and have tiny leaves with dissected margins. ELISA analyzed Gibberellic acid A1, (GA1) and A4 (GA4) contents of these transformants. In transgenic kiwifruit with severely changed morphology, GA, levels were dramatically decreased. In contrast, GA4 content was almost the same as in wild-type plants. When OSH1-transformed kiwifruit plants were treated with GA3, the defect in internode elongation was complemented and normal leaf morphology was also partly restored. Taken together, these results indicate that with respect to GA, OSH1 causes morphological changes by inhibiting the GA1 biosynthesis and does not affect GA signal transduction. | |
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