Summary auto-generated
This study presents the complete nucleotide sequences of rice grassy stunt virus (RGSV) RNA segments 5 and 6, comprising 2704 and 2584 nucleotides respectively. RGSV infects rice plants throughout southern and southeastern Asia and is transmitted by plant hoppers. The researchers determined that both RNA segments contain identical 21-nucleotide terminal sequences capable of forming panhandle-like structures through intramolecular complementarity. Each segment exhibits ambisense coding strategy, with open reading frames (ORFs) on both viral sense and complementary strands. RNA5 encodes a nucleocapsid protein (Mr 35,927) and a nonstructural protein, while RNA6 encodes a major nonstructural protein (Mr 20,581) and another protein. Notably, the predicted proteins from RGSV RNAs 5 and 6 show only distant sequence similarity (19-31% identity) to corresponding proteins encoded by RNA3 and RNA4 of other tenuiviruses such as rice stripe virus, rice hoja blanca virus, and maize stripe virus. Additionally, RGSV appears to contain six RNA segments, whereas other tenuiviruses contain four to five segments. These significant molecular differences, combined with distinct biological properties and lack of transovarial transmission, suggest RGSV warrants taxonomic classification in a separate genus rather than remaining within Tenuivirus.
Key findings
- RGSV RNA5 and RNA6 contain 21 nt complementary terminal sequences capable of forming panhandle structures and exhibit ambisense coding organization similar to other tenuiviruses
- The nucleocapsid and nonstructural proteins encoded by RGSV show only 19-31% amino acid sequence identity to corresponding proteins in rice stripe virus, rice hoja blanca virus, and maize stripe virus, compared to 48-74% identity among those three viruses
- RGSV possesses six RNA genome segments compared to four to five segments in other characterized tenuiviruses, indicating distinct genome architecture
- Molecular and biological evidence, including lack of transovarial transmission and symptomatology differences, supports reclassification of RGSV into a separate taxonomic genus
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Abstract
The genome of rice grassy stunt virus (RGSV) consists of six RNA segments. The nucleotide (nt) sequences of the two smallest segments, RNAs 5 and 6, were determined and found to comprise 2704 and 2584 nt, respectively. The 5'- and 3'-terminal sequences of both RNAs were identical over a length of 21 nt and could potentially form a panhandle- like structure due to intramolecular complementarity. Each RNA segment contained a virus (v) sense open reading frame (ORF) in the 5'- proximate region, and a virus complementary (vc) ORF in the 3'- proximate region, indicating an ambisense coding strategy. The protein encoded by the ORF on the vc strand of RNA5 was identified as the viral nucleocapsid protein (M(r) 35927). The ORF on the v strand of RNA6 encoded a protein of M(r) 20581 which represented the major nonstructural protein, previously shown to be produced in RGSV-infected rice tissues. The predicted proteins encoded by RGSV RNAs 5 and 6 were only distantly similar in sequence to the four proteins encoded by RNAs 3 and 4 of other viruses belonging to the genus Tenuivirus. These low sequence similarities, together with the apparently distinct number of genome segments, set RGSV apart from the other tenuiviruses and indicate that it should be placed in a taxonomically separate genus.