Analysis on regulation of ACC synthase gene expression during fruit ripening.

为了研究甜瓜和黄瓜果实成熟特性的差异，对果实成熟过程中ACC合成酶(ACS)基因的表达调控和乙烯受体基因的表达进行了分析。甜瓜和黄瓜果实中的acs基因在基因结构和序列上高度同源，不仅在cdna水平上，而且在基因组水平上也是如此。顺式元件分析表明，两个ACS基因的启动子中都存在许多共同的元件。Southern杂交分析表明，每个单倍体基因组都以单拷贝的形式存在。以β-葡萄糖苷酸酶(GUS)为报告基因，瞬时检测了甜瓜和黄瓜acs基因的启动子活性。黄瓜ACS基因的启动子(约2kb)CS-ACS1在成熟甜瓜果实中果皮圆盘中显示出活性。此外，通过GUS瞬时分析，甜瓜ACS1基因(CME-ACS1)和CS-ACS1基因在未成熟和成熟甜瓜和黄瓜中果皮圆盘中的启动子(约2kb)活性没有差异。对甜瓜和黄瓜的乙烯受体基因进行了Southern分析。在甜瓜和黄瓜中，乙烯受体基因ETR1和ERS1在单倍体基因组中以单拷贝形式存在，并且这两个基因在品种间具有很好的保守性。Northern杂交结果表明，ETR1和ERS1基因在黄瓜果实中的表达依赖于乙烯，这与已报道的这两个基因在甜瓜果实中的表达模式是一致的。因此，推测甜瓜和黄瓜果实在成熟过程中乙烯受体和ACS1基因转录在乙烯信号转导途径中的转录步骤之间的差异是导致甜瓜和黄瓜果实成熟特性不同的原因。

In order to investigate the difference of ripening characteristics between melon and cucumber fruits, analyses were conducted on regulation of ACC synthase (ACS) gene expression and on expression of ethylene receptor genes during fruit ripening.1. ACS genes from melon and cucumber fruits were highly homologous in terms of gene structure and sequence, not only at the cDNA but also at the genomic levels. Analysis of cis-element revealed that many common elements were present in the promoters of both ACS genes. Southern blot analysis indicated that each ACS gene was present as a single copy per haploid genome.2. Promoter activities of ACS genes from melon and cucumber were measured transiently using β- glucuronidase (GUS) as a reporter gene. Promoter (ca. 2kb) of a cucumber ACS gene, CS-ACS1, showed its activity in mesocarp disks of ripe melon fruit. In addition, there was no difference in promoter (ca. 2kb) activities between melon ACS1 gene (CMe-ACS1) and CS-ACS1 in immature and mature melon and cucumber mesocarp disks by the GUS transient assay.3. Southern analysis was conducted on ethylene receptor genes from melon and cucumber. Ethylene receptor genes, ETR1 and ERS1, were present in melon and cucumber as a single copy per haploid genome, and both genes were well conserved beyond the cultivars. Northern blotting demonstrated that expression of ETR1and ERS1 genes were ethylene-dependent in cucumber fruit, which coincided well with the already reported expression pattern of these genes in melon fruit.As a conclusion, it was presumed that the difference between melon and cucumber fruits in ripening characteristics was caused in each fruit during ripening between the steps of ethylene receptor and ACS1 gene transcription in ethylene signal transduction pathway.