Hormonal Cross-Talk Between Auxin and Ethylene Differentially Regulates the Expression of Two Members of the 1-Aminocyclopropane-1-Carboxylate Oxidase Gene Family in Rice(Oryza sativa L.)

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Two cDNA clones, pOS-ACO2 and pOS-ACO3, encoding 1-aminocyclopropane-1-carboxylate(ACC) oxidase were isolated from rice seedling cDNA library. pOS-ACO3 is a 1, 299 bp full-length clone encoding 321 amino acids(M_r=35.9 kDa), while pOS-ACO2 is 1, 072 bp long and is a partial cDNA clone encoding 314 amino acids. These two deduced amino acid sequences share 70% identity, and display a high degree of sequence identity(72-92%)with previously isolated pOS-ACO1 of deepwater rice. The chromosomal location studies show that OS-ACO2 is positioned on the long arm of chromosome 9, while OS-ACO3 on the long arm of chromosome 2 of rice genome. A marked increase in the level of OS-ACO2 transcript was observed in IAA-treated etiolated rice seedlings, whereas the OS-ACO3 mRNA was greatly accumulated by ethylene treatment. Results of ethylene inhibitor studies indicated that auxin promotion of the OS-ACO2 transcription was not mediated through the action of auxin-induced ethylene. Thus, it appears that there are two groups of ACC oxidase transcripts in rice plants, either auxin-induced or ethylene-induced. The auxin-induced OS-ACO2 expression was partially inhibited by ethylene, while ethylene induction of OS-ACO3 transcription was completely blocked by auxin. These results indicate that the expression of ACC oxidase genes is regulated by complex hormonal networks in a gene specific manner in rice seedlings. Okadaic acid, a potent inhibitor of protein phosphatase, effectively suppressed the IAA induction of OS-ACO2 expression, suggesting that protein dephosphorylation plays a role in the induction of ACC oxidase by auxin. A scheme of the multiple regulatory pathways for the expression of ACC oxidase gene family by auxin, ethylene and protein phosphatase is presented.
日本植物生理学会の論文

Hormonal Cross-Talk Between Auxin and Ethylene Differentially Regulates the Expression of Two Members of the 1-Aminocyclopropane-1-Carboxylate Oxidase Gene Family in Rice(Oryza sativa L.)

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