Gong Pichang, Ao Xiang, Liu Gaixiu, Cheng Fangyun, He Chaoying
State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
Landscape Architecture College of Beijing Forestry University, National Flower Engineering Research Center, Beijing, China.
Plant Cell Physiol. 2017 Mar 1;58(3):411-425. doi: 10.1093/pcp/pcw204.
Herbaceous peony (Paeonia lactiflora) is a globally important ornamental plant. Spontaneous floral mutations occur frequently during cultivation, and are selected as a way to release new cultivars, but the underlying evolutionary developmental genetics remain largely elusive. Here, we investigated a collection of spontaneous corolla mutational plants (SCMPs) whose other floral organs were virtually unaffected. Unlike the corolla in normal plants (NPs) that withered soon after fertilization, the transformed corolla (petals) in SCMPs was greenish and persistent similar to the calyx (sepals). Epidermal cellular morphology of the SCMP corolla was also similar to that of calyx cells, further suggesting a sepaloid corolla in SCMPs. Ten floral MADS-box genes from these Paeonia plants were comparatively characterized with respect to sequence and expression. Codogenic sequence variation of these MADS-box genes was not linked to corolla changes in SCMPs. However, we found that both APETALA3 (AP3) and PISTILLATA (PI) lineages of B-class MADS-box genes were duplicated, and subsequent selective expression alterations of these genes were closely associated with the origin of SCMPs. AP3-PI obligate heterodimerization, essential for organ identity of corolla and stamens, was robustly detected. However, selective down-regulation of these duplicated genes might result in a reduction of this obligate heterodimer concentration in a corolla-specific manner, leading to the sepaloid corolla in SCMPs, thus representing a new sepaloid corolla model taking advantage of gene duplication. Our work suggests that modifying floral MADS-box genes could facilitate the breeding of novel cultivars with distinct floral morphology in ornamental plants, and also provides new insights into the functional evolution of the MADS-box genes in plants.
芍药（Paeonia lactiflora）是一种全球重要的观赏植物。在栽培过程中，自发的花突变频繁发生，并被选作培育新品种的一种方式，但其潜在的进化发育遗传学仍 largely 难以捉摸。在这里，我们研究了一组自发花冠突变植株（SCMPs），其其他花器官几乎未受影响。与正常植株（NPs）中受精后不久就枯萎的花冠不同，SCMPs 中转化的花冠（花瓣）呈绿色且持久，类似于花萼（萼片）。SCMP 花冠的表皮细胞形态也与萼片细胞相似，进一步表明 SCMPs 中有萼片状花冠。对这些芍药属植物的 10 个花 MADS-box 基因进行了序列和表达方面的比较特征分析。这些 MADS-box 基因的编码序列变异与 SCMPs 中的花冠变化无关。然而，我们发现 B 类 MADS-box 基因的 APETALA3（AP3）和 PISTILLATA（PI）谱系均发生了复制，并且这些基因随后的选择性表达改变与 SCMPs 的起源密切相关。AP3-PI 专性异二聚化对于花冠和雄蕊的器官特性至关重要，被强烈检测到。然而，这些复制基因的选择性下调可能以花冠特异性方式导致这种专性异二聚体浓度降低，从而导致 SCMPs 中出现萼片状花冠，因此代表了一种利用基因复制的新的萼片状花冠模型。我们的工作表明，修饰花 MADS-box 基因可以促进观赏植物中具有独特花形态的新品种的培育，也为植物中 MADS-box 基因的功能进化提供了新的见解。
