Plants bearing double flowers have long been cultivated as ornamental plants. Hose-in-hose flowers, bearing 2-whorled corolla tubes in whorls 1 and 2, are uncommon but recur in Sinningia (Gesnerioideae, Gesneriaceae). In this study, we selected 15 hose-in-hose cultivars as materials to explore the underlying molecular and genetic mechanisms of this floral architecture. We found that they originated from different hybridization events within the Dircaea clade. Three B-class MADS-box genes were globally expressed in all floral whorls, but only GLOBOSA1 (GLO1) has accumulated a dominant mutation, i.e., the insertion of a hAT-like miniature inverted-repeat transposable element (MITE) into its promoter, that co-segregated with the hose-in-hose phenotype. In addition, all 15 hose-in-hose cultivars contained the same dominant GLO1 allele. Transient gene expression assays confirmed the role of this MITE insertion in up-regulating the promoter activity of GLO1 by providing several cis-regulatory elements. Genetic transformation in heterologous Chirita pumila (Didymocarpoideae, Gesneriaceae) verified that this dominant GLO1 allele is sufficient to confer the hose-in-hose phenotype. We further demonstrated that both the GLO1 allele and the hAT-like MITE descended from wild S. cardinalis with single flowers. This study highlights the significance of wide hybridization in frequent gains of the dominant GLO1 allele and thereafter repeated occurrence of hose-in-hose flowers in Sinningia.

中文翻译：

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单个显性 GLOBOSA 等位基因解释了 Sinningia （Gesneriaceae） 中软管花的重复起源


长期以来，开双花的植物一直被作为观赏植物栽培。软管花，在轮生 1 和 2 中带有 2 轮生花冠管，并不常见，但在 Sinningia（Gesnerioideae，Gesneriaceae）中会复发。在这项研究中，我们选择了 15 个 hose-in-hose 品种作为材料，以探索这种花卉结构的潜在分子和遗传机制。我们发现它们起源于 Dircaea 分支内的不同杂交事件。三个 B 类 MADS-box 基因在所有花轮中均表达，但只有 GLOBOSA1 （GLO1） 积累了显性突变，即将 hAT 样微型反向重复转座因子 （MITE） 插入其启动子中，该启动子与软管中的软管表型共分离。此外，所有 15 个软管栽培品种都包含相同的显性 GLO1 等位基因。瞬时基因表达测定证实了这种 MITE 插入通过提供几种顺式调节元件在上调 GLO1 启动子活性中的作用。异源 Chirita pumila （Didymocarpoideae， Gesneriaceae） 的遗传转化证实了这种显性 GLO1 等位基因足以赋予软管表型。我们进一步证明 GLO1 等位基因和 hAT 样 MITE 都来自单花的野生红衣主教。本研究强调了广泛杂交在显性 GLO1 等位基因频繁获得以及此后在 Sinningia 中重复出现软管花的意义。