Department of Cell Biology and Plant Biochemistry, University of Regensburg Regensburg, Germany.
Front Plant Sci. 2014 Mar 12;5:76. doi: 10.3389/fpls.2014.00076. eCollection 2014.
The diverse flowers of Orchidaceae are the result of several major morphological transitions, among them the most studied is the differentiation of the inner median tepal into the labellum, a perianth organ key in pollinator attraction. Type A peloria lacking stamens and with ectopic labella in place of inner lateral tepals are useful for testing models on the genes specifying these organs by comparing their patterns of expression between wild-type and peloric flowers. Previous studies focused on DEFICIENS- and GLOBOSA-like MADS-box genes because of their conserved role in perianth and stamen development. The "orchid code" model summarizes this work and shows in Orchidaceae there are four paralogous lineages of DEFICIENS/AP3-like genes differentially expressed in each floral whorl. Experimental tests of this model showed the conserved, higher expression of genes from two specific DEF-like gene lineages is associated with labellum development. The present study tests whether eight MADS-box candidate SEP-, FUL-, AG-, and STK-like genes have been specifically duplicated in the Orchidaceae and are also differentially expressed in association with the distinct flower organs of Phalaenopsis hyb. "Athens." The gene trees indicate orchid-specific duplications. In a way analogous to what is observed in labellum-specific DEF-like genes, a two-fold increase in the expression of SEP3-like gene PhaMADS7 was measured in the labellum-like inner lateral tepals of peloric flowers. The overlap between SEP3-like and DEF-like genes suggests both are associated with labellum specification and similar positional cues determine their domains of expression. In contrast, the uniform messenger levels of FUL-like genes suggest they are involved in the development of all organs and their expression in the ovary suggests cell differentiation starts before pollination. As previously reported AG-like and STK-like genes are exclusively expressed in gynostemium and ovary, however no evidence for transcriptional divergence was found in the stage investigated. Gene expression suggests a developmental regulatory system based on the combined activity of duplicate MADS-box genes. We discuss its feasibility based on documented protein interactions and patterns of expression.
兰科植物种类繁多，其花朵形态多样，这是多次重要形态转变的结果，其中研究最多的是中内花瓣分化为唇瓣，这是吸引传粉者的花被器官的关键。缺少雄蕊且具异位唇瓣代替内轮侧花瓣的 A 型四射花，可用于通过比较其在野生型和四射花之间的表达模式，来测试关于指定这些器官的基因的模型。以前的研究主要集中在 DEFICIENS 和 GLOBOSA 样 MADS 框基因上，因为它们在花被和雄蕊发育中具有保守作用。“兰花密码”模型总结了这方面的工作，并表明在兰科植物中，有四个 DEFICIENS/AP3 样基因的同源基因谱系在每个花轮中差异表达。对该模型的实验测试表明，两个特定的 DEF 样基因谱系的保守、高表达与唇瓣发育有关。本研究测试了 8 个 MADS 框候选 SEP、FUL、AG 和 STK 样基因是否在兰科植物中特异性复制，并且是否与蝴蝶兰杂种“雅典”的不同花器官的差异表达相关。基因树表明兰花具有特异性复制。类似于在唇瓣特异性 DEF 样基因中观察到的情况，在四射花的唇瓣样内轮侧花瓣中测量到 SEP3 样基因 PhaMADS7 的表达增加了两倍。SEP3 样和 DEF 样基因之间的重叠表明，两者都与唇瓣的特化有关，并且相似的位置线索决定了它们的表达域。相比之下，FUL 样基因的均匀信使水平表明它们参与所有器官的发育，并且它们在卵巢中的表达表明细胞分化在授粉前就开始了。如前所述，AG 样和 STK 样基因仅在雌雄蕊和卵巢中表达，但在所研究的阶段未发现转录分化的证据。基因表达表明基于重复 MADS 框基因的组合活性的发育调控系统。我们根据已记录的蛋白质相互作用和表达模式讨论了其可行性。
