Department of Biology, Kongju National University, Kongju, Korea.
PLoS One. 2013 Jul 16;8(7):e68232. doi: 10.1371/journal.pone.0068232. Print 2013.
The loss of photosynthetic function should lead to the cessation of expression and finally loss of photosynthetic genes in the new heterotroph. Dinoflagellates are known to have lost their photosynthetic ability several times. Dinoflagellates have also acquired photosynthesis from other organisms, either on a long-term basis or as "kleptoplastids" multiple times. The fate of photosynthetic gene expression in heterotrophs can be informative into evolution of gene expression patterns after functional loss, and the dinoflagellates ability to acquire new photosynthetic function through additional endosymbiosis. To explore this we analyzed a large-scale EST database consisting of 151,091 unique sequences (29,170 contigs, 120,921 singletons) obtained from 454 pyrosequencing of the heterotrophic dinoflagellate Pfiesteria piscicida. About 597 contigs from P. piscicida showed significant homology (E-value <e(-30)) with proteins associated with plastid and photosynthetic function. Most of the genes involved in the Calvin-Benson cycle were found, genes of the light-dependent reaction were also identified. Also genes of associated pathways including the chorismate pathway and genes involved in starch metabolism were discovered. BLAST searches and phylogenetic analysis suggest that these plastid-associated genes originated from several different photosynthetic ancestors. The Calvin-Benson cycle genes are mostly associated with genes derived from the secondary plastids of peridinin-containing dinoflagellates, while the light-harvesting genes are derived from diatoms, or diatoms that are tertiary plastids in other dinoflagellates. The continued expression of many genes involved in photosynthetic pathways indicates that the loss of transcriptional regulation may occur well after plastid loss and could explain the organism's ability to "capture" new plastids (i.e. different secondary endosymbiosis or tertiary symbioses) to renew photosynthetic function.
光合作用功能的丧失应该导致新异养生物中光合作用基因的表达停止，最终丢失。已知甲藻已经多次失去了光合作用能力。甲藻还通过其他生物体多次从其他生物体获得光合作用，无论是长期的还是作为“kleptoplastids”。异养生物中光合作用基因表达的命运可以为功能丧失后基因表达模式的进化提供信息，以及甲藻通过额外内共生获得新光合作用功能的能力。为了探索这一点，我们分析了一个由 454 焦磷酸测序获得的 151091 个独特序列（29170 个重叠群，120921 个单核苷酸）组成的大型 EST 数据库，这些序列来自于异养甲藻 Pfiesteria piscicida。大约 597 个来自 P. piscicida 的重叠群与与质体和光合作用功能相关的蛋白质表现出显著同源性（E 值 <e(-30))。发现了参与卡尔文-本森循环的大多数基因，还鉴定了光依赖反应的基因。还发现了相关途径的基因，包括色氨酸途径和参与淀粉代谢的基因。BLAST 搜索和系统发育分析表明，这些与质体相关的基因源自几个不同的光合作用祖先。卡尔文-本森循环基因大多与来自含有 Peridinin 的甲藻的次生质体衍生的基因相关，而光捕获基因则来自硅藻，或其他甲藻中的 tertiary plastids。许多参与光合作用途径的基因的持续表达表明转录调控的丧失可能在质体丧失后很久才发生，这可以解释生物体“捕获”新质体（即不同的二次内共生或三次共生）以更新光合作用功能的能力。
