Summary auto-generated
This study reports the complete nucleotide sequence of the large (L) genome segment of impatiens necrotic spot virus (INSV), completing the sequence of this tripartite tospovirus genome. The INSV L RNA is 8,776 nucleotides long and encodes a 2,865 amino acid protein (approximately 330 kDa) representing the viral RNA-dependent RNA polymerase, containing conserved motifs diagnostic for RNA polymerases of negative-stranded RNA viruses. The L segment was obtained from a Dutch isolate (NL-07) isolated from infected Impatiens. Comparative analysis with tomato spotted wilt virus (TSWV), another tospovirus, revealed 69% amino acid identity and 83% similarity, though the INSV L RNA is 124 nucleotides shorter and lacks the acidic C-terminal tail present in TSWV. Phylogenetic analysis of L proteins across the Bunyaviridae family reveals that tospoviruses are most closely related to the genus Bunyavirus, while tenuiviruses (another ambisense plant virus genus) cluster with Phlebovirus, suggesting these two plant-infecting genera evolved through independent evolutionary pathways from animal-infecting bunyaviruses.
Key findings
- The complete INSV genome sequence is now available, with the L segment being 8,776 nt and encoding a putative RNA-dependent RNA polymerase (330 kDa)
- INSV L RNA is 124 nt shorter than TSWV L RNA and lacks the acidic C-terminal tail, though this does not appear to affect in vitro transcription-replication activity
- Phylogenetic analysis shows tospoviruses are most closely related to Bunyavirus, while tenuiviruses are most closely related to Phlebovirus, indicating two independent evolutionary pathways for plant-infecting ambisense bunyaviruses
- The L RNA segment is the most conserved among the three INSV genome segments, while the S RNA is least conserved compared to TSWV
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Abstract
The nucleotide sequence of the large (L) genome segment of impatiens necrotic spot virus (INSV) has been determined, and herewith the complete nucleotide sequence of the whole, tripartite genome of this important tospovirus has been elucidated. The L RNA is 8776 nucleotides long and of negative polarity, containing one large ORF on the viral complementary strand. Comparison of the deduced amino acid sequence of the INSV L RNA primary translation product (330.3 kDa) with those of the L RNAs of other members of the family Bunyaviridae reveals that this protein represents the putative viral RNA-dependent RNA polymerase. A cluster dendrogram of the (putative) RNA polymerases indicates that the genera Tospovirus and Tenuivirus, though both encompassing ambisense plant-infecting viruses, have different affinities to the animal-infecting Bunyaviridae, tospoviruses being most closely related to the genus Bunyavirus, and tenuiviruses to the genus Phlebovirus.