Evolutionary Ecology Group, Naturalis Biodiversity Center, Leiden, The Netherlands.
Institute of Biology Leiden, Leiden University, Leiden, The Netherlands.
PLoS One. 2023 Oct 10;18(10):e0286846. doi: 10.1371/journal.pone.0286846. eCollection 2023.
Fruits play a crucial role in seed dispersal. They open along dehiscence zones. Fruit dehiscence zone formation has been intensively studied in Arabidopsis thaliana. However, little is known about the mechanisms and genes involved in the formation of fruit dehiscence zones in species outside the Brassicaceae. The dehiscence zone of A. thaliana contains a lignified layer, while dehiscence zone tissues of the emerging orchid model Erycina pusilla include a lipid layer. Here we present an analysis of evolution and development of fruit dehiscence zones in orchids. We performed ancestral state reconstructions across the five orchid subfamilies to study the evolution of selected fruit traits and explored dehiscence zone developmental genes using RNA-seq and qPCR. We found that erect dehiscent fruits with non-lignified dehiscence zones and a short ripening period are ancestral characters in orchids. Lignified dehiscence zones in orchid fruits evolved multiple times from non-lignified zones. Furthermore, we carried out gene expression analysis of tissues from different developmental stages of E. pusilla fruits. We found that fruit dehiscence genes from the MADS-box gene family and other important regulators in E. pusilla differed in their expression pattern from their homologs in A. thaliana. This suggests that the current A. thaliana fruit dehiscence model requires adjustment for orchids. Additionally, we discovered that homologs of A. thaliana genes involved in the development of carpel, gynoecium and ovules, and genes involved in lipid biosynthesis were expressed in the fruit valves of E. pusilla, implying that these genes may play a novel role in formation of dehiscence zone tissues in orchids. Future functional analysis of developmental regulators, lipid identification and quantification can shed more light on lipid-layer based dehiscence of orchid fruits.
水果在种子传播中起着至关重要的作用。它们沿着开裂区域打开。拟南芥中的果实开裂区域形成已得到深入研究。然而，对于拟南芥以外物种的果实开裂区域形成的机制和基因知之甚少。拟南芥的开裂区域包含木质化层，而新兴兰花模式 Erycina pusilla 的开裂区域组织包含脂质层。在这里，我们分析了兰花果实开裂区域的进化和发育。我们在五个兰花亚科中进行了祖先状态重建，以研究选定果实特征的进化，并使用 RNA-seq 和 qPCR 探索开裂区域发育基因。我们发现，直立开裂的果实、无木质化开裂区域和较短的成熟时间是兰花的祖先特征。兰花果实的木质化开裂区域是从无木质化区域多次进化而来的。此外，我们对来自不同发育阶段的 E. pusilla 果实组织进行了基因表达分析。我们发现，来自 MADS 框基因家族的果实开裂基因和 E. pusilla 中的其他重要调节因子在表达模式上与拟南芥的同源物不同。这表明目前的拟南芥果实开裂模型需要针对兰花进行调整。此外，我们发现参与心皮、雌蕊和胚珠发育以及参与脂质生物合成的拟南芥基因的同源物在 E. pusilla 的果实瓣中表达，这表明这些基因可能在兰花开裂区域组织的形成中发挥新的作用。对发育调节剂、脂质鉴定和定量的未来功能分析可以更深入地了解兰花果实基于脂质层的开裂。
