| 摘要： ‘香拔’番石榴（Psidium guajava L.）為非更年型‘珍珠拔’番石榴芽條變異所選育的品種，其 果實後熟階段呼吸與乙烯生成速率顯著上升，伴隨著果皮轉色、質地軟化，並揮發出濃郁香氣， 呈現典型更年型番石榴後熟特徵，然而其果實後熟特性不同於‘珍珠拔’母本的原因尚未有研究報 導，目前推測認為原坐落於‘珍珠拔’系統-2 ACC（1-aminocyclopropane-1-carboxylic acid）合成 酶（ACC synthase; ACS）基因PgACS1 啟動子區的反轉錄轉位子（retrotransposon），在芽變 株‘香拔’已跳離，使得‘香拔’PgACS1 恢復正常基因表現，得以合成大量ACC 提供乙烯生合成所 致。為檢視前述假說，本計劃擬將比較‘香拔’與其母株‘珍珠拔’果實生長與品質變化之生理及乙烯 生合成路徑關鍵酵素ACS 與ACC 氧化酶（ACO）酵素活性與基因表現之差異，進而選殖‘香 拔’PgACS1 基因啟動子核甘酸序列，與‘珍珠拔’PgACS1 基因進行比對，釐清反轉錄轉位子對番 石榴果實PgACS1 基因啟動子調控的角色及其對後熟特性的影響。本計劃結果除了闡釋番石榴 品種間不同後熟性狀的分子機制外，亦可應用於番石榴雜交育種計劃後裔早（苗）期選拔果實後 熟特徵之篩檢DNA 標記。‘Shiang Bar’ (SB) guava (Psidium guajava L.) was derived from a bud sport mutation of ‘Jen-Ju Bar’, (JJB), a non-climacteric cultivar. SB fruit exhibited typical climacteric ripening behaviors of guava, including increases of respiration and ethylene production rate, peel coloration, texture softening, and volatile emission. However, the mechanism that the ripening pattern of SB is different from that of JJB, the stock plant, has not been reported so far. According to the working hypothesis postulated by my group, the retrotransposon inserting into the promoter region of JJB PgACS1, a System-2 ACC (1-aminocyclopropane-1-carboxylic acid) synthase (ACS) gene, has been jumped out in the case of SB; therefore, the gene expression of SB’s PgACS1 resumed and, as a consequence, massive ACC is produced and provided for ethylene biosynthesis. In order to test the hypothesis, this proposal will investigate the physiology of fruit development and quality changes as well as enzymatic activities and gene expressions of the key enzymes in ethylene synthetic pathway, namely ACS and ACC oxidase (ACO), in both SB and JJB fruits. Furthermore, the nucleotide sequence of promoter region of SB PgACS1 will be cloned and compared with that of JJB PgACS1, which will illustrate the role of the retrotransposon in regulating PgACS1 expression and ripening pattern of guava fruit. The results of this research will not only to clarify the underline molecular mechanism of different ripening behavior among guava varieties, but also to utilizing as a molecular marker for early (seedling) stage selection among progeny in a breeding program. |
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