RESUMO
In nature, rice tungro disease is caused by an RNA and a DNA virus complex, but we have obtained an independently infectious clone of rice tungro bacilliform virus (RTBV) DNA. Infectivity could be demonstrated only when a more than unit-length copy was cloned in the Agrobacterium binary vector Bin 19 and agroinoculated into rice plants. Rice plants thus agroinfected with cloned RTBV DNA showed typical symptoms of tungro disease, presence of viral DNA and bacilliform particles, and could be used as a source of virus to infect healthy plants by the green leafhopper (Nephotettix virescens). The importance of this infectious clone in understanding the molecular biology of RTBV and the rice tungro disease is discussed.
Assuntos
DNA Viral/genética , Oryza/microbiologia , Doenças das Plantas , Vírus de Plantas/genética , Rhizobium/genética , Transfecção , Microscopia Eletrônica , Vírus de Plantas/patogenicidade , Vírus de Plantas/ultraestrutura , Plasmídeos , Mapeamento por RestriçãoRESUMO
The nucleotide sequence of an infectious clone of rice tungro bacilliform virus (RTBV) DNA has been determined. The circular genome has 8002 bp and one strand contains four open reading frames (ORFs). One ORF is potentially capable of encoding a protein of 24 kD (P24) and has no initiation (ATG) codon. The other three ORFs potentially encode proteins of 12 kD, 194 kD and 46 kD (P12, P194, P46) respectively. The functions of P24, P12 and P46 are unknown. Comparative analyses with retroviruses and Commelina yellow mottle virus suggest that the 194 kD putative product is a polyprotein that is proteolytically cleaved to yield the virion coat protein, a protease and replicase (reverse transcriptase and RNase H) characteristic of retroelements. The DNA sequence reveals other features which strongly support our belief that RTBV is a pararetrovirus. These include sequences at the mapped positions of two discontinuities in the virion DNA which are complementary to tRNA metinit and purine-rich, and may be the priming sites for minus- and plus-strand DNA synthesis respectively. As the positions of likely transcriptional signals suggest, a full-length viral transcript is observed by northern analysis. The predicted folding of the 645 bp 5'-region of this RNA resembles that of caulimoviruses. Comparisons with other reverse transcribing elements are discussed.
Assuntos
Vírus de DNA/genética , Genes Virais , Vírus de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , Sítios de Ligação , Northern Blotting , DNA Viral , Éxons , Íntrons , Dados de Sequência Molecular , Fases de Leitura Aberta , Oryza/microbiologia , Homologia de Sequência do Ácido Nucleico , Moldes GenéticosRESUMO
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 caulimoviruses. 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.
