| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 89 === Banana genomic clones λABC13, 14, 18, 98-1 and 123 isolated by using banana ABC transporter homology cDNA clone pBER44 as probe, can be classified into two groups based on restriction site maps and Southern analysis. All three clones λABC18, 98-1, 123 contain the full-length of pBER44 cDNA. λABC123 possesses more 5’ upstream sequence than λABC18 and 98-1. The banana ABC transporter gene consists of at least 24 exons and 23 introns with consensus GT-AG dinucleotides locating at their boundaries. The putative banana ABC transporter consists of 1,425 amino acids with a calculated molecular mass of 161 kDa and a predicted isoelectric point of 7.09. It contains two copies each of two structural units, a peripherally located ATP binding domain and a highly hydrophobic transmembrane domain with six transmembrane-spanning α-helices, and displays similarity to the typical structure and domain organization of the yeast PDR5 gene family. The amino acid sequence of banana ABC transporter shows at least 69 % homology to ABC transporter from Arabidopsis, rice, Nicotiana plumbaginifolia (NpABC1) and Spirodela polyrrhiza (TUR2). According to the result of promoter sequence analysis, a putative TATA box is 1263-1269 bp upstream the translation start site. Several consersved elements responsive to ABA, GA and low temperature are found in the promoter region. Northern blot analysis indicates that banana ABC transporter gene expression was induced by drought in leaves, and the mRNA accumulated abundantly in the pulp at ripening stage 7 and peel at ripening stage 5. Repression of banana ABC transporter gene expression by low temperature is consistent with fruit ripening. No obvious gene expression was detected in banana fruit at ripening stage 1 by different concentrations of ABA treatment for 12 hours. Accumulation of banana ABC transporter mRNA was enhanced in fruits at ripening stage 5 treated with 10-3M BA, 10-3M ABA or 10-1M NaCl for 12 hours. However, its expression was reduced by 10-3M IAA treatment.
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