Hunan Vegetable Research Institute, Hunan Academy of Agricultural Sciences, Changsha 410125, China.
Key Laboratory of Biology and Genetic Improvement of Horticultural Crops of the Ministry of Agriculture, Sino-Dutch Joint Laboratory of Horticultural Genomics, Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Mol Plant. 2016 Sep 6;9(9):1315-1327. doi: 10.1016/j.molp.2016.06.018. Epub 2016 Jul 9.
Sex determination in plants gives rise to unisexual flowers that facilitate outcrossing and enhance genetic diversity. In cucumber and melon, ethylene promotes carpel development and arrests stamen development. Five sex-determination genes have been identified, including four encoding 1-aminocyclopropane-1-carboxylate (ACC) synthase that catalyzes the rate-limiting step in ethylene biosynthesis, and a transcription factor gene CmWIP1 that corresponds to the Mendelian locus gynoecious in melon and is a negative regulator of femaleness. ACC oxidase (ACO) converts ACC into ethylene; however, it remains elusive which ACO gene in the cucumber genome is critical for sex determination and how CmWIP1 represses development of female flowers. In this study, we discovered that mutation in an ACO gene, CsACO2, confers androecy in cucumber that bears only male flowers. The mutation disrupts the enzymatic activity of CsACO2, resulting in 50% less ethylene emission from shoot tips. CsACO2 was expressed in the carpel primordia and its expression overlapped with that of CsACS11 in female flowers at key stages for sex determination, presumably providing sufficient ethylene required for proper CsACS2 expression. CmACO3, the ortholog of CsACO2, showed a similar expression pattern in the carpel region, suggesting a conserved function of CsACO2/CmACO3. We demonstrated that CsWIP1, the ortholog of CmWIP1, could directly bind the promoter of CsACO2 and repress its expression. Taken together, we propose a presumably conserved regulatory module consisting of WIP1 transcription factor and ACO controls unisexual flower development in cucumber and melon.
植物的性别决定产生单性花，有利于异交，提高遗传多样性。在黄瓜和甜瓜中，乙烯促进心皮发育，阻止雄蕊发育。已经鉴定出五个性别决定基因，包括四个编码 1-氨基环丙烷-1-羧酸（ACC）合酶的基因，该酶催化乙烯生物合成的限速步骤，以及一个转录因子基因 CmWIP1，它对应于甜瓜中的孟德尔基因座位雌性，是雌性的负调节剂。ACC 氧化酶（ACO）将 ACC 转化为乙烯；然而，黄瓜基因组中哪个 ACO 基因对性别决定至关重要，以及 CmWIP1 如何抑制雌花发育，这仍然难以捉摸。在这项研究中，我们发现 ACO 基因（CsACO2）的突变赋予了黄瓜雄性，只开雄花。该突变破坏了 CsACO2 的酶活性，导致茎尖的乙烯释放减少 50%。CsACO2 在心皮原基中表达，其表达与 CsACS11 在性别决定的关键阶段在雌花中重叠，可能为适当的 CsACS2 表达提供所需的足够乙烯。CsACO2 的同源物 CmACO3 在心皮区域表现出相似的表达模式，表明 CsACO2/CmACO3 具有保守功能。我们证明了 CmWIP1 的同源物 CsWIP1 可以直接结合 CsACO2 的启动子并抑制其表达。总之，我们提出了一个推测的保守调控模块，由 WIP1 转录因子和 ACO 组成，控制黄瓜和甜瓜的单性花发育。
