Summary auto-generated
Rice tungro disease, a major virus disease of rice in southeast Asia causing over $1.5 billion in annual losses, results from infection by two distinct viruses: rice tungro spherical virus (RTSV) and rice tungro bacilliform virus (RTBV). This study characterized the molecular properties of both viruses. RTSV was identified as a single-stranded, polyadenylated RNA virus with a genome size of approximately 10 kilobases, containing two coat proteins of 35K and 26K molecular weight. RTBV was characterized as a double-stranded circular DNA virus with a genome of 8.3 kilobases, containing two major coat proteins of 37K and 33K, along with minor protein species. The RTBV DNA structure resembles that of caulimoviruses, possessing two discontinuities (gaps) at specific sites, one in each strand. These discontinuities are characteristic of pararetroviruses that replicate via reverse transcription. The discovery that RTBV is a DNA virus with caulimoviruses-like properties, infecting a monocot crop, has significant implications for understanding plant virus evolution and potentially for developing genetic engineering strategies for rice and other cereal crops.
Key findings
- Rice tungro spherical virus (RTSV) is a single-stranded, polyadenylated RNA virus with a ~10 kb genome
- Rice tungro bacilliform virus (RTBV) contains a double-stranded circular DNA genome of 8.3 kb with two strand-specific discontinuities, resembling caulimoviruses
- RTSV has coat proteins of 35K and 26K; RTBV has major coat proteins of 37K and 33K
- RTBV shares structural features with pararetroviruses, suggesting it may replicate via reverse transcription
- The two viruses causing rice tungro are fundamentally different in genome type and structure, requiring co-infection for severe disease
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Abstract
We present evidence that rice tungro spherical virus (RTSV) has a genome of polyadenylated single-stranded RNA of about 10 kb whereas rice tungro bacilliform virus (RTBV) contains double-stranded circular DNA. RTBV DNA has been mapped and shown to have two discontinuities, one in each strand, at specific sites; it thus resembles that of the caulimo-viruses. Gel electrophoresis of RTSV preparations revealed two protein bands (Mr 35K and 26K). RTBV yielded two major protein bands of 37K and 33K together with several minor species of higher and lower Mr which react with antiviral serum.
† Present address: Department of Biochemistry, University of Cambridge, Cambridge, U.K.