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

为探讨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）基因表达调控和乙烯受体基因表达调控进行了分析。甜瓜和黄瓜果实的ACS基因不仅在cDNA水平上，而且在基因组水平上都具有高度的同源性。顺式元件分析表明，两个ACS基因的启动子中存在许多共同元件。Southern blot分析表明，每个ACS基因在每个单倍体基因组中以一个拷贝的形式存在。以β-葡萄糖醛酸酶（GUS）为报告基因，对甜瓜和黄瓜的ACS基因启动子活性进行了瞬时测定。黄瓜ACS基因CS-ACS1启动子（约2kb）在成熟甜瓜果实中果皮盘上显示出活性。另外，GUS瞬时检测结果显示，甜瓜ACS1基因（CMe-ACS1）和CS-ACS1在未成熟和成熟甜瓜和黄瓜中果皮盘上的启动子（约2kb）活性无显著差异。对甜瓜和黄瓜的乙烯受体基因进行了南方分析。乙烯受体基因ETR1和ERS1存在于甜瓜和黄瓜的单倍体基因组中，且这两个基因在不同品种间具有较好的保守性。Northern blotting结果表明，黄瓜果实中etr1和ERS1基因的表达是乙烯依赖的，这与已有报道的甜瓜果实中这两个基因的表达模式相吻合。由此推测，甜瓜和黄瓜果实成熟特性的差异是由于果实成熟过程中乙烯受体和乙烯信号转导通路中ACS1基因转录步骤之间的差异造成的。

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.