中科院武汉植物园高磊博士等人在王艇研究员指导下，发现蕨类叶绿体基因组的进化动态远比以往设想的更为复杂。研究结果已于4月13日发表在国际学术刊物BMC Plant Biology。
武汉植物园在前期的研究中测定了我国首个蕨类植物叶绿体基因组全序列（BMC Evolutionary Biology, 2009, 9:130），并注意到位于蕨类叶绿体基因组大单拷贝区的rpoB和psbZ间区（BZ区），其基因顺序可归为两类：一是以观音座莲和松叶蕨为代表的祖先型，即座莲型；一是以桫椤和铁线蕨为代表的衍生型，称为铁线蕨型。分析认为，从座莲型到铁线蕨型的转变可能是借助两条进化途径、依靠两次部分重叠的倒位得以实现，但是对该结构性重组的具体进化过程尚不了解。
为解决此问题，武汉植物园高磊博士等人在王艇研究员指导下，以BZ区为对象，对涵盖现存蕨类所有11个目的植物进行了测序和进化基因组学分析，发现除树蕨类、水龙骨类和异孢蕨类组成的核心薄囊蕨以外，所有其他蕨类均表现为座莲型；而绝大多数核心薄囊蕨类则拥有铁线蕨型。出乎意料的是，树蕨类华东瘤足蕨（Plagiogyria japonica）的基因顺序（瘤足蕨型）与前二者均不相同，有可能是在铁线蕨型基础上再发生一次小型回复倒位所致。在膜蕨类的南海瓶蕨（Vandenboschia radicans）和木贼类的问荆（Equisetum arvense）及节节草（Equisetum ramosissimum）的trnY-trnE基因间区（YE-IGS）中观察到有大量重复序列存在。南海瓶蕨的YE-IGS含17个高度相似、大小为27 bp的串联重复；它们与相邻的trnY-GUA基因的反密码子区同源，并都能形成类似的茎环结构。问荆和节节草的YE-IGS极度扩张至5kb，拥有上百个可形成茎环二级结构的散布重复，其序列组成和结构也同邻近trnY的反密码子区高度同源。
此外，该研究还证实蕨类的trnD-GUC基因发生过一次倒位以及ycf66在蕨类中曾被多次丢失。这些结果对深入理解蕨类植物叶绿体基因组的进化具重要意义。
中山大学生命科学学院苏应娟教授课题组参与了部分研究工作。（生物谷Bioon.com）
生物谷推荐原文出处：
BMC Plant Biology 2011, 11:64doi:10.1186/1471-2229-11-64
Evolution of the rpoB-psbZ region in fern plastid genomes: notable structural rearrangements and highly variable intergenic spacers
Lei Gao , Yuan Zhou , Zhi-Wei Wang , Ying-Juan Su and Ting Wang
Background
The rpoB-psbZ (BZ) region of some fern plastid genomes (plastomes) has been noted to go through considerable genomic changes. Unraveling its evolutionary dynamics across all fern lineages will lead to clarify the fundamental process shaping fern plastome structure and organization.
Results
A total of 24 fern BZ sequences were investigated with taxon sampling covering all the extant fern orders. We found that: (i) a tree fern Plagiogyria japonica contained a novel gene order that can be generated from either the ancestral Angiopteris type or the derived Adiantum type via a single inversion; (ii) the trnY-trnE intergenic spacer (IGS) of the filmy fern Vandenboschia radicans was expanded 3-fold due to the tandem 27-bp repeats which showed strong sequence similarity with the anticodon domain of trnY; (iii) the trnY-trnE IGSs of two horsetail ferns Equisetum ramosissimum and E. arvense underwent an unprecedented 5-kb long expansion, more than a quarter of which was consisted of a single type of direct repeats also relevant to the trnY anticodon domain; and (iv) ycf66 has independently lost at least four times in ferns.
Conclusions
Our results provided fresh insights into the evolutionary process of fern BZ regions. The intermediate BZ gene order was not detected, supporting that the Adiantum type was generated by two inversions occurring in pairs. The occurrence of Vandenboschia 27-bp repeats represents the first evidence of partial tRNA gene duplication in fern plastomes. Repeats potentially forming a stem-loop structure play major roles in the expansion of the trnY-trnE IGS.
