Helper component for aphid transmission encoded by region II of cauliflower mosaic virus DNA

Two mutant strains of beet necrotic yellow vein virus (BNYVV) containing deletion mutants of RNA-2 were produced during serial passage in mechanically inoculated Tetragonia expansa leaves. The mutant strains were referred to as S-0a (RNA-1 +2a) and G-0b (RNA-1 +2b). RNA-2a and RNA-2b were about 4.3 kb and 4-2 kb in length, respectively, whereas normal sized RNA-2 was about 4.8 kb in length. In vitro translation and immunoblot analysis showed that RNA-2, RNA2a and RNA-2b all directed synthesis of the coat protein (Mr 22K). However, whereas wild-type RNA-2 also directed the synthesis of a coat protein readthrough protein with an Mr of 83K (predicted Mr 75K), RNA-2a and RNA-2b directed the production of readthrough proteins with Mrs of 67K and 58K, respectively. This suggests that the deleted regions of RNA-2a and RNA-2b occur within the second open reading frame, which encodes a polypeptide of Mr 54K, which is translated by readthrough of the coat protein cistron. After the addition of wild-type RNA-3 and RNA-4 to all the strains, the mutant strains could not be transmitted by Polymyxa betae zoospores produced from either zoosporangia or resting spores, whereas the wild-type strains were readily transmitted. These results indicate that the 75K readthrough protein encoded by RNA-2 is essential for the transmission of BNYVV by P. betae.

Section: Discussionmentioning

confidence: 99%

Evidence that the 75K readthrough protein of beet necrotic yellow vein virus RNA-2 is essential for transmission by the fungus Polymyxa betae

Tamada

Kusume

1991

“…A delay in symptom appearance was noted for DNAs with mutations in ORF II, ORF IV and ORF VII (Armour et al, 1983;Dixon et al, 1983Dixon et al, , 1986. The DNAs mutated in ORF VII only became infectious after a second mutation had occurred in the plant restoring an altered initiation codon (Dixon et al, 1986).…”

mentioning

confidence: 97%

“…The extra 1 bp deletion about four codons 5' of the 77 bp deletion restored the original reading frame, allowing ORF II translation to end one nucleotide away from the ORF III AUG. The delayed appearance of symptoms when plants were inoculated with pSA103 DNA (Armour et al, 1983) may thus have been due to the time required for a suppressor mutation to appear.…”

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confidence: 99%

“…These observations resemble those with synthetic templates in mammalian cells (Kozak, 1984) and suggest that some of the CaMV polypeptides may be translated from a polycistronic messenger RNA (K. Sieg & B. Gronenborn, unpublished; cited in Dixon & Hohn, 1984). Infection with pSA103 was delayed relative to infection following inoculation with wild-type DNA (Armour et al, 1983). Nucleotide sequencing across the deletion in pSA103 (Fig.…”

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confidence: 99%

See 1 more Smart Citation

Infectious and Non-infectious Mutants of Cauliflower Mosaic Virus DNA

Melcher

Steffens

Lyttle

et al. 1986

SUMMARYMutants of cauliflower mosaic virus (CaMV), generated in vitro by modification of recombinant DNA plasmids containing the viral genome, either retained the ability to induce disease symptoms on turnip plants, produced less severe symptoms or failed to induce symptoms. Wild-type symptoms were produced by a variant CaMV DNA of the Cabbage S isolate that had 4 bp in open reading frame (ORF) III replaced with a 16 bp sequence. Less severe symptoms, due to a delay in symptom appearance relative to inoculation with wild-type DNA, were induced by a mutant with a frameshift mutation in ORF II (pSA103). CaMV DNA, recovered from plants infected with pSA103, contained a second mutation which restored the original translation reading frame. Nucleic acid hybridization to 'squishes' of leaf tissue from plants that had been inoculated with mutant DNAs that included DNAs modified in each of the six major ORFs of CaMV DNA revealed that only those plants that appeared diseased had detectable CaMV nucleic acid in uninoculated leaves. Replicated CaMV DNA was also not detected in non-encapsidated and virion DNA fractions from inoculated leaves of non-diseased plants.

“…Lung & Pirone (1974) reported that aphid transmission of CaMV requires an aphid transmission factor (ATF). The finding that active ATF is expressed from open reading frame (ORF) II of the CaMV genome in a baculovirus system (Blanc et al, 1993a) directly shows that ATF of CaMV is the product of ORF II, a protein of M r 18K (p18) detected in infected plant leaves (Armour et al, 1983.…”

mentioning

confidence: 99%

Reasons for the low accumulation level of aphid transmission factor protein in infected leaves with an aphid-non-transmissible cauliflower mosaic virus isolate, CM1841

Nakayashiki

Tsuge

Kobayashi

et al. 1993

The synthesis and accumulation of aphid transmission factor protein (p18) in cauliflower mosaic virus (CaMV)-infected turnip protoplasts were examined in time course and pulse-labelling experiments, comparing an aphidnon-transmissible isolate (CM1841) with an in vitro recombinant aphid-transmissible CaMV (CMBX) generated from the CM1841 isolate. There was little difference in the synthesis and accumulation of p18 between CM1841-and CMBX-infected protoplasts. When the accumulation of p18 in infected leaves was monitored from 3 to 28 days post-symptom emergence (p.e.) by Western blotting, the amount of p18 accumulated in CM 1841-infected leaves continuously decreased from 3 days p.e. throughout the experimental period, whereas the amount of p18 in CMBX-infected leaves was lowest at 3 days p.e. and increased thereafter. These results suggested that CM 1841 differed from CMBX not in the synthesis of p18 but in the stability of p18 in infected leaves.