Zhang Z, Green B R, Cavalier-Smith T
Canadian Institute for Advanced Research Evolutionary Biology Programme, Department of Botany, University of British Columbia, Vancouver.
Nature. 1999 Jul 8;400(6740):155-9. doi: 10.1038/22099.
Photosynthetic dinoflagellates are important aquatic primary producers and notorious causes of toxic 'red tides'. Typical dinoflagellate chloroplasts differ from all other plastids in having a combination of three envelope membranes and peridinin-chlorophyll a/c light-harvesting pigments. Despite evidence of a dinoflagellete satellite DNA containing chloroplast genes, previous attempts to obtain chloroplast gene sequences have been uniformly unsuccessful. Here we show that the dinoflagellate chloroplast DNA genome structure is unique. Complete sequences of chloroplast ribosomal RNA genes and seven chloroplast protein genes from the dinoflagellate Heterocapsa triquetra reveal that each is located alone on a separate minicircular chromosome: 'one gene-one circle'. The genes are the most divergent known from chloroplast genomes. Each circle has an unusual tripartite non-coding region (putative replicon origin), which is highly conserved among the nine circles through extensive gene conversion, but is very divergent between species. Several other dinoflagellate species have minicircular chloroplast genes, indicating that this type of genomic organization may have evolved in ancestral peridinean dinoflagellates. Phylogenetic analysis indicates that dinoflagellate chloroplasts are related to chromistan and red algal chloroplasts and supports their origin by secondary symbiogenesis.
光合甲藻是重要的水生初级生产者，也是有毒“赤潮”的臭名昭著的成因。典型的甲藻叶绿体与所有其他质体不同，它具有三层包膜膜和多甲藻素 - 叶绿素a/c捕光色素的组合。尽管有证据表明甲藻卫星DNA含有叶绿体基因，但先前获取叶绿体基因序列的尝试均未成功。在这里，我们表明甲藻叶绿体DNA基因组结构是独特的。来自三角异帽藻的叶绿体核糖体RNA基因和七个叶绿体蛋白基因的完整序列表明，每个基因都单独位于一个独立的小环状染色体上：“一个基因一个环”。这些基因是叶绿体基因组中已知的最具分歧性的基因。每个环都有一个不寻常的三联体非编码区域（假定的复制子起源），通过广泛的基因转换在九个环中高度保守，但在物种之间差异很大。其他几种甲藻物种也有小环状叶绿体基因，这表明这种基因组组织类型可能在祖先多甲藻目甲藻中就已进化。系统发育分析表明，甲藻叶绿体与色藻和红藻叶绿体有关，并支持它们通过次生共生起源。
