Takano Hiroyoshi, Takechi Katsuaki
Bioelectrics Research Center, Kumamoto University, Kumamoto 860-8555, Japan.
Biochim Biophys Acta. 2010 Feb;1800(2):144-51. doi: 10.1016/j.bbagen.2009.07.020. Epub 2009 Aug 6.
It is now widely accepted that an endosymbiotic cyanobacterium evolved into the plastid of the primary photosynthetic eukaryotes: glaucocystophytes, red algae, and green plants. It has been thought that during the evolution of plants, the peptidoglycan wall (or murein) was lost from the endosymbiont immediately after the branching off of the glaucocystophytes, which have peptidoglycan-armed plastids termed cyanelles. However, we found that the moss Physcomitrella patens has all of the genes for peptidoglycan biosynthesis with the exception of one racemase. The aim of the present review is to summarize recent findings on plastid peptidoglycan and to present a hypothesis for the evolution of plastids containing peptidoglycan. Gene knockout experiments for the Mur(ein) genes, including MurE in P. patens, showed that the peptidoglycan synthesis pathway is related to plastid division, although no structure can be detected between the inner and outer envelopes of the chloroplasts by electron microscopy. On the other hand, MurE in Arabidopsis thaliana has a function in plastid gene expression and not in division. Based on data regarding plant genomes and antibiotic treatment experiments of plastid division, we propose that the loss of peptidoglycan occurred independently at least three times during plant evolution: from the lineage of red algae, from the chlorophytes, and during land plant evolution.
现在人们普遍认为，一种内共生蓝细菌进化成了主要光合真核生物（蓝隐藻、红藻和绿色植物）的质体。人们一直认为，在植物进化过程中，蓝隐藻分支出去后，内共生体的肽聚糖壁（或胞壁质）立即消失，蓝隐藻具有被称为蓝小体的带有肽聚糖的质体。然而，我们发现小立碗藓除了一种消旋酶外，拥有肽聚糖生物合成的所有基因。本综述的目的是总结关于质体肽聚糖的最新发现，并提出一个关于含有肽聚糖的质体进化的假说。对包括小立碗藓中的MurE在内的Mur（胞壁质）基因进行的基因敲除实验表明，肽聚糖合成途径与质体分裂有关，尽管通过电子显微镜在叶绿体的内外膜之间未检测到结构。另一方面，拟南芥中的MurE在质体基因表达中起作用，而不是在分裂中起作用。基于有关植物基因组的数据和质体分裂的抗生素处理实验，我们提出肽聚糖的丢失在植物进化过程中至少独立发生了三次：从红藻谱系、绿藻以及陆地植物进化过程中。
