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KMID : 0368420010440020111
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Journal of Plant Biology
2001 Volume.44 No. 2 p.111 ~ p.117
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Characterization and Light-Induced Expression of the S-Adenosylmethionine Decarboxylase Gene from Ipomoea nil
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Park, Won Keun
Lee, Sun Hi/Park, Ky Young
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Abstract
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We screened a genomic library of Japanese morning glory (Ipomoea nil) and isolated the MGSDCg1 clone (GenBank Accession Number U64927). The genomic clone comprised four exons and three introns. MGSDCg1 contained a 660-bp 5´-untranslated region (UTR), a 1089-bp coding region of 362 amino acids, and a 209-bp 3´-UTR. A TATA box sequence (TATATAA) was found at position -29. The transcript leader of this SAMDC gene contained a short, upstream open reading frame (uORF) of 51 amino acids, which was interrupted with a 107-bp intron. Two other introns were positioned upstream of the uORF in the 5´-UTR. Six-day-old seedlings were grown under a 12-h light/dark cycle, then treated with white light The amount of SAMDC transcript dramatically increased from the first hour after light exposure, then returned to a basal level. SAMDC mRNA was accumulated more under high rather than low irradiance. These results suggest a relationship between photo-response and the physiological role of polyamines (PAs). The level of SAMDC mRNA was increased only by brassinosteroids, not by any other plant hormone such as kinetin, IAA, ABA, and GA. This hormonal response may have replaced the effect of light on SAMDC gene expression in the dark. PAs decreased the SAMDC mRNA level, which could then be restored by their inhibitors. This indicates that SAMDC gene expression is regulated by its cellular contents.
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