Citerne Hélène L, Reyes Elisabeth, Le Guilloux Martine, Delannoy Etienne, Simonnet Franck, Sauquet Hervé, Weston Peter H, Nadot Sophie, Damerval Catherine
Génétique Quantitative et Evolution-Le Moulon, INRA, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91190 Gif-sur-Yvette, France
Laboratoire Ecologie, Systématique et Evolution, UMR 8079 Université Paris-Sud, CNRS, AgroParisTech, 91405 Orsay, France.
Ann Bot. 2017 Feb;119(3):367-378. doi: 10.1093/aob/mcw219. Epub 2016 Dec 26.
The basal eudicot family Proteaceae (approx. 1700 species) shows considerable variation in floral symmetry but has received little attention in studies of evolutionary development at the genetic level. A framework for understanding the shifts in floral symmetry in Proteaceae is provided by reconstructing ancestral states on an upated phylogeny of the family, and homologues of CYCLOIDEA (CYC), a key gene for the control of floral symmetry in both monocots and eudicots, are characterized.
Perianth symmetry transitions were reconstructed on a new species-level tree using parsimony and maximum likelihood. CYC-like genes in 35 species (31 genera) of Proteaceae were sequenced and their phylogeny was reconstructed. Shifts in selection pressure following gene duplication were investigated using nested branch-site models of sequence evolution. Expression patterns of CYC homologues were characterized in three species of Grevillea with different types of floral symmetry.
Zygomorphy has evolved 10-18 times independently in Proteaceae from actinomorphic ancestors, with at least four reversals to actinomorphy. A single duplication of CYC-like genes occurred prior to the diversification of Proteaceae, with putative loss or divergence of the ProtCYC1 paralogue in more than half of the species sampled. No shifts in selection pressure were detected in the branches subtending the two ProtCYC paralogues. However, the amino acid sequence preceding the TCP domain is strongly divergent in Grevillea ProtCYC1 compared with other species. ProtCYC genes were expressed in developing flowers of both actinomorphic and zygomorphic Grevillea species, with late asymmetric expression in the perianth of the latter.
Proteaceae is a remarkable family in terms of the number of transitions in floral symmetry. Furthermore, although CYC-like genes in Grevillea have unusual sequence characteristics, they display patterns of expression that make them good candidates for playing a role in the establishment of floral symmetry.
基部真双子叶植物山龙眼科（约1700种）在花对称性上表现出相当大的差异，但在基因水平的进化发育研究中很少受到关注。通过在该科更新的系统发育树上重建祖先状态，为理解山龙眼科花对称性的转变提供了一个框架，并对CYCLOIDEA（CYC）的同源基因进行了表征，CYC是控制单子叶植物和真双子叶植物花对称性的关键基因。
使用简约法和最大似然法在一个新的物种水平树上重建花被对称性转变。对山龙眼科35个物种（31个属）中的CYC样基因进行测序，并重建其系统发育。使用序列进化的嵌套分支位点模型研究基因复制后选择压力的变化。在三种具有不同花对称性类型的银桦属物种中表征CYC同源基因的表达模式。
在山龙眼科中，两侧对称花已从辐射对称祖先独立进化了10 - 18次，至少有四次向辐射对称的逆转。在山龙眼科多样化之前发生了一次CYC样基因的复制，在所采样的一半以上物种中，ProtCYC1旁系同源基因存在假定的丢失或分化。在两个ProtCYC旁系同源基因的分支中未检测到选择压力的变化。然而，与其他物种相比，银桦属ProtCYC1中TCP结构域之前的氨基酸序列差异很大。ProtCYC基因在辐射对称和两侧对称的银桦属物种的发育花中均有表达，在后者的花被中表现为后期不对称表达。
就花对称性的转变次数而言，山龙眼科是一个显著的科。此外，尽管银桦属中的CYC样基因具有不寻常的序列特征，但它们显示出的表达模式使其成为在花对称性建立中发挥作用的良好候选基因。
