Genes Sufficient for Synthesizing Peptidoglycan are Retained in Gymnosperm Genomes, and MurE from Larix gmelinii can Rescue the Albino Phenotype of Arabidopsis MurE Mutation
Genes Sufficient for Synthesizing Peptidoglycan are Retained in Gymnosperm Genomes, and MurE from Larix gmelinii can Rescue the Albino Phenotype of Arabidopsis MurE Mutation
复制标题
裸子植物基因组中保留了足以合成肽聚糖的基因，落叶松MurE可挽救拟南芥MurE突变的白化表型
DOI：
10.1093/pcp/pcx005
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发表时间：
2017-03-01
影响因子：
4.9
通讯作者：
Takano, Hiroyoshi
中科院分区：
文献类型：
--
作者：
Lin, Xiaofei;Li, Ningning;Takano, Hiroyoshi
内共生理论认为，叶绿体起源于具有细胞壁的单一蓝藻祖先。细菌细胞壁的主要成分--肽聚糖(PG)在质体进化过程中逐渐降解。尽管被子植物基因组中的许多PG合成Mur基因已经丢失，但已被发现保留在基本的链柄植物的基因组中。细菌Mure基因编码的酶催化细菌PG生物合成中UDP-N-乙酰胞壁酸(UDPMurNAc)三肽的形成。Mure基因的敲除导致了叶绿体分裂的缺陷，而T-DNA标记的拟南芥Mure突变体对叶绿体的发育有抑制作用，但不抑制叶绿体的分裂，这表明AtMurE在功能上与细菌和苔藓Mure蛋白不同。在这里，我们可以在最近测序的云杉和火炬松基因组中鉴定出包括Mure在内的10个细菌Mur基因的同源物，这表明裸子植物中保留了质体PG系统。为了研究裸子植物Mure的功能，我们从落叶松(Larix gmelinii，LgMurinii)中分离出一个Mure的同源基因，并证实其在落叶松幼苗叶片中以单拷贝形式存在，并且在落叶松幼苗的叶片中大量表达。结合绿色荧光蛋白和LgMurE的融合蛋白分析表明，它定位于叶绿体中。与拟南芥和矮牵牛Mure突变体的跨种互补分析表明，LgMurE基因的表达完全挽救了拟南芥的反照性缺陷，但不能挽救矮牵牛的大叶绿体表型。结合不同进化阶段植物基因组的信息，讨论了叶绿体PG的进化和Mure基因功能差异的机制。
The endosymbiotic theory states that plastids are derived from a single cyanobacterial ancestor that possessed a cell wall. Peptidoglycan ( PG), the main component of the bacteria cell wall, gradually degraded during plastid evolution. PG-synthesizing Mur genes have been found to be retained in the genomes of basal streptophyte plants, although many of them have been lost from the genomes of angiosperms. The enzyme encoded by bacterial MurE genes catalyzes the formation of the UDP-N-acetylmuramic acid (UDPMurNAc) tripeptide in bacterial PG biosynthesis. Knockout of the MurE gene in the moss Physcomitrella patens resulted in defects of chloroplast division, whereas T-DNA-tagged mutants of Arabidopsis thaliana for MurE revealed inhibition of chloroplast development but not of plastid division, suggesting that AtMurE is functionally divergent from the bacterial and moss MurE proteins. Here, we could identify 10 homologs of bacterial Mur genes, including MurE, in the recently sequenced genomes of Picea abies and Pinus taeda, suggesting the retention of the plastid PG system in gymnosperms. To investigate the function of gymnosperm MurE, we isolated an ortholog of MurE from the larch, Larix gmelinii (LgMurE) and confirmed its presence as a single copy per genome, as well as its abundant expression in the leaves of larch seedlings. Analysis with a fusion protein combining green fluorescent protein and LgMurE suggested that it localizes in chloroplasts. Cross-species complementation assay with MurE mutants of A. thaliana and P. patens showed that the expression of LgMurE cDNA completely rescued the albefaction defects in A. thaliana but did not rescue the macrochloroplast phenotype in P. patens. The evolution of plastid PG and the mechanism behind the functional divergence of MurE genes are discussed in the context of information about plant genomes at different evolutionary stages.