We investigated the histology and developmental morphology of flowers of wild‐rice (Zizania aquatica), a member of grass subfamily Oryzoideae, to determine whether male flowers in this species develop in a manner similar to those in the subfamily Panicoideae, a group that includes many species with unisexual flowers. Zizania has evolved unisexual flowers from hermaphrodite ancestors and is only distantly related to the Panicoideae; the origins of unisexual flowers are independent in the two taxa. Ontogenetic evidence indicates that many species within the subfamily Panicoideae develop male flowers by a process similar to that already described for maize (Zea mays), a panicoid grass. Unisexual male flowers in maize initiate both the stamen (androecium) and the pistil (gynoecium), but the gynoecium aborts early in development through the death of the subepidermal cells. Cell death in gynoecia of maize is known to be controlled by the product of the gene tasselseed2 (ts2), and an orthologue of ts2 has been shown to have the same effect in the sister genus Tripsacum. It seems likely that ts2 orthologues mediate cell death throughout the Panicoideae, but the phylogenetic range of the cell death mechanism is not known. In this study we show that male flowers of Z. aquatica show neither the distinctive pattern of cell death nor the ontogenetic timing of abortion that are characteristic of male flower formation in studied species of Panicoideae. This indicates that these unisexual flowers may be produced by an entirely different mechanism from that employed by the Panicoideae. Either ts2 does not control sex expression in Zizania, or it is deployed at a different time, and possibly in different tissues, with a different histological result. Our results indicate that the independent origins of male flowers in Gramineae apparently do not have a common system of genetic control.

中文翻译：

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茭白（北美野生稻；禾本科）雄花的发育

我们研究了草亚科 Oryzoideae 的成员野水稻（Zizania Aquatica）的花的组织学和发育形态，以确定该物种的雄花是否以类似于 Panicoideae 亚科的方式发育，该亚科包括许多具有单性花的物种。Zizania 已经从雌雄同体的祖先进化出单性花，并且与 Panicoideae 的亲缘关系很远。单性花的起源在两个分类群中是独立的。个体发育证据表明，Panicoideae 亚科中的许多物种通过类似于已经描述的玉米（Zea mays）（一种禾本科植物）的过程来发育雄花。玉米中的单性雄花启动雄蕊（androecium）和雌蕊（gynoecium），但是由于表皮下细胞的死亡，雌蕊在发育早期就中止了。已知玉米雌蕊中的细胞死亡是由基因 tasselseed2 (ts2) 的产物控制的，并且 ts2 的直向同源物已被证明在姊妹属 Tripsacum 中具有相同的效果。似乎 ts2 直向同源物介导了整个 Panicoideae 的细胞死亡，但细胞死亡机制的系统发育范围尚不清楚。在这项研究中，我们表明水生 Z.aquatica 的雄花既没有表现出独特的细胞死亡模式，也没有表现出所研究的 Panicoideae 种雄性花形成特征的个体发育时间流产。这表明这些单性花的产生机制可能与 Panicoideae 所采用的机制完全不同。ts2 要么不控制 Zizania 中的性表达，要么在不同的时间部署，并且可能在不同的组织中部署，具有不同的组织学结果。我们的结果表明禾本科雄花的独立起源显然没有共同的遗传控制系统。