Cloning of cDNAs for DELLA proteins suppressing cysteine proteinase genes in germinated cotyledons of common bean seeds

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Gibberellins (GAs) are involved in the expression of cysteine proteinase genes in germinated cotyledons of common bean seeds. Because DELLA proteins are known to be transcriptional repressors mediating GA signaling, we isolated two cDNA clones encoding DELLA proteins (PvGAI1 and PvGAI2) from common bean seedlings to examine the mechanism of GA signaling involved in the expression of the proteinase genes. RT-PCR and RNA blot analyses indicated that the level of mRNA in germinated cotyledons was higher for PvGAI2 than for PvGAI1. We also found that transient expression of PvGAI2, but not that of PvGAI1, repressed the promoter activities of GA-inducible cysteine proteinase genes, EP-C1 and CP2, in germinated cotyledons. These findings suggest that PvGAI2 is mainly responsible for regulating the expression of proteinase genes in germinated cotyledons. Application of a GA-biosynthesis inhibitor, prohexadione calcium to common bean seeds had little effect on the RNA level of PvGAI2, although the inhibitor repressed genes for EP-C1 and CP2. Because it is known that GA induces degradation of DELLA proteins, our findings suggest that the level of GA, but not the mRNA expression of PvGAI2, regulates the protein level of PvGAI2 suppressing the proteinases genes in germinated cotyledons.
日本植物細胞分子生物学会の論文
2007-12-01