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Abstract：
In cellular organisms, inosine triphosphate pyrophosphatases (ITPases) prevent the incorporation of mutagenic deaminated purines into nucleic acids. These enzymes have also been detected in the genomes of several plant RNA viruses infecting two euphorbia species. In particular, two ipomoviruses produce replicase-associated ITPases to cope with high concentration of non-canonical nucleotides found in cassava tissues.
Using high-throughput RNA sequencing on the wild euphorbia species Mercurialis perennis, two new members of the families Potyviridae and Secoviridae were identified. Both viruses encode for a putative ITPase, and were found in mixed infection with a new partitivirid. Following biological and genomic characterization of these viruses, the origin and function of the phytoviral ITPases were investigated.
While the potyvirid was shown to be pathogenic, the secovirid and partitivirid could not be transmitted. The secovirid was found belonging to a proposed new Comovirinae genus tentatively named \"Mercomovirus\", which also accommodates other viruses identified through transcriptome mining, and for which an asymptomatic pollen-associated lifestyle is suspected. Homology and phylogenetic analyses inferred that the ITPases encoded by the potyvirid and secovirid were likely acquired through independent horizontal gene transfer events, forming lineages distinct from the enzymes found in cassava ipomoviruses. Possible origins from cellular organisms are discussed for these proteins. In parallel, the endogenous ITPase of M. perennis was predicted to encode for a C-terminal nuclear localization signal, which appears to be conserved among the ITPases of euphorbias but absent in other plant families. This subcellular localization is in line with the idea that nucleic acids remain protected in the nucleus, while deaminated nucleotides accumulate in the cytoplasm where they act as antiviral molecules.
Three new RNA viruses infecting M. perennis are described, two of which encoding for ITPases. These enzymes have distinct origins, and are likely required by viruses to circumvent high level of cytoplasmic non-canonical nucleotides. This putative plant defense mechanism has emerged early in the evolution of euphorbias, and seems to specifically target certain groups of RNA viruses infecting perennial hosts.
Using high-throughput RNA sequencing on the wild euphorbia species Mercurialis perennis, two new members of the families Potyviridae and Secoviridae were identified. Both viruses encode for a putative ITPase, and were found in mixed infection with a new partitivirid. Following biological and genomic characterization of these viruses, the origin and function of the phytoviral ITPases were investigated.
While the potyvirid was shown to be pathogenic, the secovirid and partitivirid could not be transmitted. The secovirid was found belonging to a proposed new Comovirinae genus tentatively named \"Mercomovirus\", which also accommodates other viruses identified through transcriptome mining, and for which an asymptomatic pollen-associated lifestyle is suspected. Homology and phylogenetic analyses inferred that the ITPases encoded by the potyvirid and secovirid were likely acquired through independent horizontal gene transfer events, forming lineages distinct from the enzymes found in cassava ipomoviruses. Possible origins from cellular organisms are discussed for these proteins. In parallel, the endogenous ITPase of M. perennis was predicted to encode for a C-terminal nuclear localization signal, which appears to be conserved among the ITPases of euphorbias but absent in other plant families. This subcellular localization is in line with the idea that nucleic acids remain protected in the nucleus, while deaminated nucleotides accumulate in the cytoplasm where they act as antiviral molecules.
Three new RNA viruses infecting M. perennis are described, two of which encoding for ITPases. These enzymes have distinct origins, and are likely required by viruses to circumvent high level of cytoplasmic non-canonical nucleotides. This putative plant defense mechanism has emerged early in the evolution of euphorbias, and seems to specifically target certain groups of RNA viruses infecting perennial hosts.
摘要：
背景：在细胞生物中，三磷酸肌苷焦磷酸酶（ITPases）可防止诱变脱氨基嘌呤掺入核酸中。这些酶也已在感染两种大孔草物种的几种植物RNA病毒的基因组中检测到。特别是,两种ipomovirus产生与复制酶相关的ITP酶，以应对木薯组织中发现的高浓度非规范核苷酸。
方法：使用高通量RNA测序对野生大孔菌属水龙，确定了Potyviridae和Secoviridae的两个新成员。两种病毒都编码一种推定的ITPase，并被发现与一种新的偏分体混合感染。根据这些病毒的生物学和基因组特征，研究了植物病毒ITPase的起源和功能。
结果：虽然发现potyvirid具有致病性，Secovirid和partivirid无法传播。发现该病毒属于拟议的新的Comovirinae属，暂定名为“Mercomovirus”，它还容纳通过转录组挖掘鉴定的其他病毒，并且怀疑无症状的花粉相关生活方式。同源性和系统发育分析推断，由potyvirid和secovirid编码的ITP酶可能是通过独立的水平基因转移事件获得的，形成与木薯共形病毒中发现的酶不同的谱系。讨论了这些蛋白质的可能来源。并行,预测PerennisM.的内源性ITPase编码C末端核定位信号，这似乎是保守的，但在其他植物家族的ITPase中不存在。这种亚细胞定位符合核酸在细胞核中保持保护的想法，而脱氨基的核苷酸在细胞质中积累，在那里它们充当抗病毒分子。
结论：描述了三种感染PerennisM.的新RNA病毒，其中两个编码为ITPase。这些酶有不同的起源，并且可能是病毒所必需的，以规避高水平的细胞质非规范核苷酸。这种推定的植物防御机制已经在欣快感的进化早期出现，并且似乎专门针对感染多年生宿主的某些RNA病毒组。
方法：使用高通量RNA测序对野生大孔菌属水龙，确定了Potyviridae和Secoviridae的两个新成员。两种病毒都编码一种推定的ITPase，并被发现与一种新的偏分体混合感染。根据这些病毒的生物学和基因组特征，研究了植物病毒ITPase的起源和功能。
结果：虽然发现potyvirid具有致病性，Secovirid和partivirid无法传播。发现该病毒属于拟议的新的Comovirinae属，暂定名为“Mercomovirus”，它还容纳通过转录组挖掘鉴定的其他病毒，并且怀疑无症状的花粉相关生活方式。同源性和系统发育分析推断，由potyvirid和secovirid编码的ITP酶可能是通过独立的水平基因转移事件获得的，形成与木薯共形病毒中发现的酶不同的谱系。讨论了这些蛋白质的可能来源。并行,预测PerennisM.的内源性ITPase编码C末端核定位信号，这似乎是保守的，但在其他植物家族的ITPase中不存在。这种亚细胞定位符合核酸在细胞核中保持保护的想法，而脱氨基的核苷酸在细胞质中积累，在那里它们充当抗病毒分子。
结论：描述了三种感染PerennisM.的新RNA病毒，其中两个编码为ITPase。这些酶有不同的起源，并且可能是病毒所必需的，以规避高水平的细胞质非规范核苷酸。这种推定的植物防御机制已经在欣快感的进化早期出现，并且似乎专门针对感染多年生宿主的某些RNA病毒组。
