甜瓜是重要的经济作物和深受世界人民喜爱的果品。糖含量是影响甜瓜果实品质的主要因素，研究甜瓜糖积累和代谢机制对改善果实品质具有重要的理论和实践意义。目前甜瓜糖代谢的分子遗传学研究较少。本文通过甜瓜糖代谢关键酶——酸性转化酶和己糖激酶基因的克隆、功能鉴定和表达调控的分析，初步研究了不同品种甜瓜果实中糖分积累与酸性转化酶和己糖激酶的关系。本研究对比不同物种的酸性转化酶序列后，根据蛋白保守序列设计出简并引物，通过PCR反应获得目的基因片断，然后利用RACE技术克隆得到了甜瓜酸性转化酶基因CmInv1的全长序列。CmInv1包含2043 bp的开放阅读框，编码的蛋白含680个氨基酸，具有糖基水解酶即β-呋喃果糖苷酶的特征结构域，这表明CmInv1是甜瓜的酸性转化酶。通过半定量RT-PCR分析CmInv1基因在甜瓜不同组织中的表达模式，发现该基因仅在花和果实当中表达。对05-21和4A1562两个品种甜瓜果实的糖含量进行测定，对比CmInv1在果实不同发育时期的表达模式发现：在甜瓜果实发育早期，转化酶的转录活性较低；5 DAP后，随着转化酶转录活性的升高，蔗糖含量下降，葡萄糖和果糖含量上升；15 DAP时，05-21中CmInv1表达量下降，蔗糖含量开始上升, 而此时在4A1562中CmInv1表达量上升，蔗糖含量没有变化；25 DAP以后，两个品种中CmInv1表达量均下降，05-21蔗糖含量继续升高，而4A1562变化很小。由此可见甜瓜果实糖的含量和组成与CmInv1有明显的相关性，推测CmInv1可能对果实发育和糖积累有重要作用。本研究在拼接前期工作获得的cDNA序列后，PCR克隆了两个甜瓜己糖激酶基因HXK1、HXK2序列全长（FJ231522和FJ231523）。HXK1、HXK2基因开放阅读框均为1497 bp，分别编码498个氨基酸。 HXK1、HXK2能够与酵母缺陷型三重突变体YSH7.4-3C (hxk1, hxk2, glk1) 进行功能互补，证明其具有己糖激酶的活性。半定量RT-PCR分析结果显示：HXK1在花中表达量较高，可能对甜瓜花器官发育和成熟具有功能；HXK2在库组织器官中表达量较高，可能与库器官建成是相关的。结合果实糖含量分析，认为HXKs与甜瓜果实中己糖的含量相关。综合分析得到：CmInv1和HXKs可能对甜瓜果实品质形成具有重要作用。

Melon is an important economic crop， and also a popular fruit for people all over the world. The quality of melon fruit depends on the sugar content that is decided by the key enzymes related to sugar metabolism. However, studies of molecular genetics especially on melon sucrose metabolism are limited. To investigate the mechanism of sugar metabolism, acid invertase and two hexokinases in melon fruit were isolated. Then gene functions and expression patterns in different cultivars of melons were analysed to reveal the regulation function of the key enzymes.Degenerate oligonucleotide primers based on the conserved amino acid motifs of acid invertase in plants were used to amplify cDNA sequence from Cucumis melo, and the full-length cDNA sequence of the invertase was obtained by RACE, designated as CmInv1. This gene contained an open reading frame (ORF) of 2043 bp, which encoded 680 amino acids. It included a glycosyl hydrolase domain that was the identification of this gene’s function. The expression of CmInv1 examined by RT-PCR in different tissues of melon showed that it expressed only in flowers and fruits.The sugar content and gene expression patterns in two cultivars (05-21, 4A1562) were compared, and the results showed that: in the early stage of fruit development, CmInv1 had low transcriptional activity and the fruits had high sucrose content; from 5 DAP, with the increase of transcriptional activity of CmInv1, sucrose content decreased, whereas glucose and fructose contents increased; up to 15 DAP, transcriptional activity of CmInv1 in 05-21 decreased, and sucrose content began to increase, while 4A1562 had opposite results at the same time; after 25 DAP, transcriptional activity of CmInv1 decreased in both cultivars, and sucrose content in 05-21 kept increasing. Therefore, there was a significant relationship between CmInv1 and sugar content in melon fruit, which inferred the special function of this gene in fruit development.After the splicing of the cDNA fragments obtained before, two full length melon hexokinases cDNA were isolated, designated as HXK1 and HXK2 (FJ231522 and FJ231523). ORFs of both two HXKs were 1497 bp, encoding 498 amino acids respectively. The hexokinase activity of the HXKs was confirmed by functional complementation of the hexokinase-deficient yeast strain YSH7.4-3C (hxk1, hxk2, glk1).The expression patterns of HXKs in different tissues examined by RT-PCR showed that: HXK1 mainly expressed in flowers，which implied the special features of HXK1 in flower organ development; HXK2 expressed highly in roots, stems, flowers and fruits indicating its roles in sink organ construction. Combined with sugar content analysis in two cultivas, it is implied that HXKs were related to hexose content in melon fruit.Taken together, the CmInv1 and HXKs may play important roles in sugar content of melon fruit.