Ethylene is an important regulatory phytohormone for sex differentiation and flower development. As the rate-limiting enzyme encoding genes in ethylene biosynthesis, ACS gene family has been well studied in cucumber; however, little is known in other cucurbit crops, such as melon and watermelon, which show diverse sex types in the field. Here, we identified and characterized eight ACS genes each in the genomes of melon and watermelon. According to the conserved serine residues at C-terminal, all the ACS genes could be characterized into three groups, which were supported by the exon–intron organizations and conserved motif distributions. ACS genes displayed diverse tissue-specific expression patterns among four melon and three watermelon sex types. Furthermore, a comparative expression analysis in the shoot apex identified orthologous pairs with potential functions in sex determination, e.g., ACS1s and ACS6s. All ACS orthologs in melon and watermelon exhibited similar expression patterns in monoecious and gynoecious genotypes, except for ACS11s and ACS12s. As expected, the majority of ACS genes were responsive to exogenous ethephon; however, some orthologs exhibited opposite expression patterns, such as ACS1s, ACS9s, and ACS10s. Collectively, our findings provide valuable ACS candidates related to flower development in various sex types of melon and watermelon.

乙烯是性别分化和花发育的重要调节植物激素。作为乙烯生物合成中编码基因的限速酶，ACS基因家族在黄瓜中得到了很好的研究；然而，对其他葫芦科作物知之甚少，如甜瓜和西瓜，它们在田间表现出不同的性别类型。在这里，我们鉴定并表征了甜瓜和西瓜基因组中的8 个ACS基因。根据C末端保守的丝氨酸残基，所有ACS基因可以分为三组，这得到外显子-内含子组织和保守基序分布的支持。ACS基因在四种甜瓜和三种西瓜性别类型中显示出不同的组织特异性表达模式。此外，茎尖中的比较表达分析确定了在性别决定中具有潜在功能的直系同源对，例如，ACS1s和ACS6s。除了ACS11s和ACS12s之外，甜瓜和西瓜中的所有ACS直向同源物在雌雄同株和雌雄同株基因型中都表现出相似的表达模式。正如预期的那样，大多数ACS基因对外源乙烯利有反应。然而，一些直系同源物表现出相反的表达模式，例如ACS1s、ACS9s和ACS10s. 总的来说，我们的研究结果提供了与甜瓜和西瓜的各种性别类型的花发育相关的有价值的ACS候选者。