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烟草的叶绿体DNA基因组,标示于内侧的基因位于DNA的同一股上,标示于外侧者则位于另一股,基因中的缺口为内含子

叶绿体DNA(Chloroplast DNA,cpDNA)为真核生物细胞叶绿体内的DNA。叶绿体等质粒体中具有一独立于细胞核基因组,且含有核糖体翻译合成自身的蛋白质[1][2],为一半自主的细胞器,叶绿体DNA最早于1959年透过生化实验发现[3],并于1962年透过电子显微镜实际观测确认[4]。1986年烟草地钱英语Marchantia polymorpha的叶绿体DNA被测序发表,为最早完成测序的叶绿体基因组[5][6],目前已有大量陆生植物与藻类英语List of sequenced plastomes的质粒体被测序发表。

基因组结构 编辑

叶绿体DNA为环状,长度一般介于120至170kb之间[7][8][9],分子量为8000万至1.3亿Da[10],多数植物的叶绿体包含约120个基因[11][12],大多编码光合作用所需的蛋白(包括RuBisCO的大次单元)与基因表达所需的蛋白[13],如4种rRNA、约30种tRNA、21种核糖体蛋白以及叶绿体RNA聚合酶的4个次单元[13]。绝大多数生物的叶绿体DNA均不分段,双鞭毛虫门的藻类则为罕见例外,此类生物的叶绿体DNA包括约40段质粒,每个质粒长2至10kb,包含1至3个基因,也有些质粒不编码任何基因[14]

多数叶绿体DNA包括两段反向重复序列(IRa与IRb),将叶绿体DNA分成大单拷贝区(LSC)与小单拷贝区(SSC)两区域[9]。反向重复序列长4至25kb,其中植物的一般在20至25kb之间[15],IRa与IRb的序列一般会因协同演化英语Concerted evolution而非常近似[14]。植物叶绿体DNA的反向重复序列演化上相当保守[9][15]蓝菌基因组与灰藻红藻的叶绿体基因组中也有与其同源的序列,显示此序列在演化上的起源很早,在叶绿体出现前即已存在[14]。有些叶绿体(豌豆与数种红藻[14])的基因组丢失了反向重复序列[15][16]紫菜属英语Porphyra红藻叶绿体则有一个重复序列发生了倒转,使IRa与IRb变为同向排列[14]。反向重复序列可能可帮助维持叶绿体DNA的稳定[16]

陆生植物新叶的叶绿体中一般有约100个叶绿体DNA,老叶中则仅剩15至20个[17],多包裹成拟核,一个叶绿体中常有数个拟核[10]。叶绿体DNA虽不与组蛋白结合[18],但红藻的叶绿体DNA可编码和组蛋白相似的组蛋白样叶绿体蛋白(HC)与自身结合[19]。较原始的红藻Cyanidioschyzon merolae英语Cyanidioschyzon merolae(属温泉红藻纲)的叶绿体拟核集中在叶绿体基質的中央,绿藻与陆生植物的叶绿体拟核则均匀分布于基質中[19]

 
模式植物拟南芥的叶绿体DNA基因组

参见 编辑

参考文献 编辑

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