Research on the regulation of gibberellin receptors

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Arabidopsis carries three receptor genes for the phytohormone gibberellin (GA), AtGID1a, AtGID1b, and AtGID1c. The expression of each gene in the rice gid1-1 mutant for GA-receptor reverts its severely dwarfed phenotype and GA-insensitivity to a normal level, even though each loss-of-function mutant shows no clear phenotype in Arabidopsis. We report the functional redundancy and specificity of each AtGID1 by analyzing the multiple mutants for loss-of-function mutation. Seeds of double KO mutants, atgid1a+atgid1b, atgid1a+atgid1c, and atgid1b+atgid1c, normally germinated. The double KO mutant, atgid1a+atgid1c showed a dwarf phenotype, while other double mutants had a normal height comparable to the wild type. Stamens of the double KO mutant, atgid1a+atgid1b are significantly much shorter than those of wild type, and this leads to low fertility A severe disarrangement of the pattern on its seed surface was also observed. The triple KO mutant, atgid1a+atgid1b+atgid1c did not germinate voluntarily, but could only start to grow when the seed coat was peeled off after soaking. Seedlings of the triple KO mutants were severe dwarfs several millimeters high after growing for one month. Moreover the triple KO seedlings completely lost their ability to respond to exogenously applied GA. These results show that all AtGID1s function as GA receptors in Arabidopsis, and in part have specific role(s) for growth and development.