71. シロイヌナズナのジベレリン代謝酵素AtGA2ox7は高塩ストレス時の積極的な生長抑制に関与する

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When exposed to salinity stress, plants retard their growth and become compact in consequence. This is regarded as one of the stress adaptations, but molecular mechanism of the growth retardation has been largely unknown. We have reported that overexpression of salinity-responsive DDF1 gene, encoding a putative AP2 transcription factor of DREB1/CBF subfamily, causes dwarfism mainly through a reduction of bioactive gibberellins (GAs) in transgenic Arabidopsis. Microarray analysis showed that the AtGA2ox7 gene, encoding a catabolic enzyme of precursor GA, was strongly upregulated in the transgenic plants. The expression of RGL3, coding for a putative negative regulator of GA signaling, was also induced. Transient overexpression of DDF1 induced the promoter activity of AtGA2ox7 and RGL3 in Arabidopsis leaves. A loss-of-function mutation of AtGA2ox7 (atga2ox7-2) suppressed the dwarf phenotype of transgenic plants overexpressing DDF1, indicating that DDF1 causes GA deficiency by induction of AtGA2ox7. In Arabidopsis treated with high-salinity stress, AtGA2ox7 and RGL3 genes were upregulated. Furthermore, AtGA2ox7-2 mutant showed less retarded growth than wild type under high-salinity stress. These results indicate that, under high-salinity stress, Arabidopsis actively reduces endogenous GA levels for growth retardation by transcriptional activation of AtGA2ox7.
植物化学調節学会の論文
2005-10-13