United States Department of Agriculture, Agricultural Research Service, Molecular Plant Pathology Laboratory, Beltsville, Maryland, United States of America.
PLoS One. 2011;6(8):e23289. doi: 10.1371/journal.pone.0023289. Epub 2011 Aug 18.
An intracellular plant pathogen 'Candidatus Liberibacter asiaticus,' a member of the Rhizobiales, is related to Sinorhizobium meliloti, Bradyrhizobium japonicum, nitrogen fixing endosymbionts, Agrobacterium tumefaciens, a plant pathogen, and Bartonella henselae, an intracellular mammalian pathogen. Whole chromosome comparisons identified at least 50 clusters of conserved orthologous genes found on the chromosomes of all five metabolically diverse species. The intracellular pathogens 'Ca. Liberibacter asiaticus' and Bartonella henselae have genomes drastically reduced in gene content and size as well as a relatively low content of guanine and cytosine. Codon and amino acid preferences that emphasize low guanosine and cytosine usage are globally employed in these genomes, including within regions of microsynteny and within signature sequences of orthologous proteins. The length of orthologous proteins is generally conserved, but not their isoelectric points, consistent with extensive amino acid substitutions to accommodate selection for low GC content. The 'Ca. Liberibacter asiaticus' genome apparently has all of the genes required for DNA replication present in Sinorhizobium meliloti except it has only two, rather than three RNaseH genes. The gene set required for DNA repair has only one rather than ten DNA ligases found in Sinorhizobium meliloti, and the DNA PolI of 'Ca. Liberibacter asiaticus' lacks domains needed for excision repair. Thus the ability of 'Ca. Liberibacter asiaticus' to repair mutations in its genome may be impaired. Both 'Ca. Liberibacter asiaticus and Bartonella henselae lack enzymes needed for the metabolism of purines and pyrimidines, which must therefore be obtained from the host. The 'Ca. Liberibacter asiaticus' genome also has a greatly reduced set of sigma factors used to control transcription, and lacks sigma factors 24, 28 and 38. The 'Ca. Liberibacter asiaticus' genome has all of the hallmarks of a reduced genome of a pathogen adapted to an intracellular lifestyle.
一种细胞内植物病原体“亚洲韧皮杆菌”，属于根瘤菌目，与苜蓿中华根瘤菌、大豆根瘤菌、固氮共生体、根癌农杆菌、植物病原体和巴尔通体属亨氏内细菌有关。全染色体比较确定，在所有五种代谢不同的物种的染色体上发现了至少 50 个保守直系同源基因簇。细胞内病原体“亚洲韧皮杆菌”和巴尔通体属亨氏内细菌的基因组在基因含量和大小上严重减少，并且鸟嘌呤和胞嘧啶含量相对较低。这些基因组在全球范围内使用了强调低鸟嘌呤和胞嘧啶使用的密码子和氨基酸偏好，包括微同线区域和直系同源蛋白的特征序列内。直系同源蛋白的长度通常是保守的，但等电点不是，这与适应低 GC 含量选择的广泛氨基酸取代一致。“亚洲韧皮杆菌”基因组显然包含了苜蓿中华根瘤菌中所有用于 DNA 复制的基因，但它只有两个而不是三个 RNaseH 基因。用于 DNA 修复的基因集在苜蓿中华根瘤菌中只有一个而不是十个 DNA 连接酶，并且“亚洲韧皮杆菌”的 DNA PolI 缺乏用于切除修复的结构域。因此，“亚洲韧皮杆菌”修复其基因组中突变的能力可能受损。“亚洲韧皮杆菌”和巴尔通体属亨氏内细菌都缺乏代谢嘌呤和嘧啶所需的酶，因此必须从宿主中获得。“亚洲韧皮杆菌”基因组也大大减少了用于转录控制的 sigma 因子，并且缺乏 sigma 因子 24、28 和 38。“亚洲韧皮杆菌”基因组具有病原体适应细胞内生活方式的减少基因组的所有特征。
