中科院武漢植物園高磊博士等人在王艇研究員指導(dǎo)下，發(fā)現(xiàn)蕨類葉綠體基因組的進(jìn)化動態(tài)遠(yuǎn)比以往設(shè)想的更為復(fù)雜,。研究結(jié)果已于4月13日發(fā)表在國際學(xué)術(shù)刊物BMC Plant Biology,。
武漢植物園在前期的研究中測定了我國首個蕨類植物葉綠體基因組全序列（BMC Evolutionary Biology, 2009, 9:130）,，并注意到位于蕨類葉綠體基因組大單拷貝區(qū)的rpoB和psbZ間區(qū)（BZ區(qū)），其基因順序可歸為兩類：一是以觀音座蓮和松葉蕨為代表的祖先型,，即座蓮型,；一是以桫欏和鐵線蕨為代表的衍生型，稱為鐵線蕨型,。分析認(rèn)為,，從座蓮型到鐵線蕨型的轉(zhuǎn)變可能是借助兩條進(jìn)化途徑、依靠兩次部分重疊的倒位得以實(shí)現(xiàn),，但是對該結(jié)構(gòu)性重組的具體進(jìn)化過程尚不了解,。
為解決此問題，武漢植物園高磊博士等人在王艇研究員指導(dǎo)下,，以BZ區(qū)為對象,，對涵蓋現(xiàn)存蕨類所有11個目的植物進(jìn)行了測序和進(jìn)化基因組學(xué)分析，發(fā)現(xiàn)除樹蕨類、水龍骨類和異孢蕨類組成的核心薄囊蕨以外,，所有其他蕨類均表現(xiàn)為座蓮型,；而絕大多數(shù)核心薄囊蕨類則擁有鐵線蕨型。出乎意料的是,，樹蕨類華東瘤足蕨（Plagiogyria japonica）的基因順序（瘤足蕨型）與前二者均不相同,，有可能是在鐵線蕨型基礎(chǔ)上再發(fā)生一次小型回復(fù)倒位所致。在膜蕨類的南海瓶蕨（Vandenboschia radicans）和木賊類的問荊（Equisetum arvense）及節(jié)節(jié)草（Equisetum ramosissimum）的trnY-trnE基因間區(qū)（YE-IGS）中觀察到有大量重復(fù)序列存在,。南海瓶蕨的YE-IGS含17個高度相似,、大小為27 bp的串聯(lián)重復(fù)；它們與相鄰的trnY-GUA基因的反密碼子區(qū)同源,，并都能形成類似的莖環(huán)結(jié)構(gòu),。問荊和節(jié)節(jié)草的YE-IGS極度擴(kuò)張至5kb，擁有上百個可形成莖環(huán)二級結(jié)構(gòu)的散布重復(fù),，其序列組成和結(jié)構(gòu)也同鄰近trnY的反密碼子區(qū)高度同源,。
此外，該研究還證實(shí)蕨類的trnD-GUC基因發(fā)生過一次倒位以及ycf66在蕨類中曾被多次丟失,。這些結(jié)果對深入理解蕨類植物葉綠體基因組的進(jìn)化具重要意義,。
中山大學(xué)生命科學(xué)學(xué)院蘇應(yīng)娟教授課題組參與了部分研究工作。（生物谷Bioon.com）
生物谷推薦原文出處：
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.
