Widely separated sequence elements within cucumber mosaic virus satellites contribute to their ability to induce lethal tomato necrosis

Abstract

To determine the structural requirements for cucumber mosaic virus (CMV) satellites to elicit lethal tomato necrosis, three satellite variants D, S and Y were used in the construction and cloning of chimeric cDNAs. D and S are necrogenic and non-necrogenic 'prototype' variants, respectively, and Y possesses the 3' conserved necrosis-determining region but does not cause lethal tomato necrosis. Its 5' half harbours an insertion/ deletion region that results in a molecule about 30 nucleotides longer than other variants. Tomato bioassays were conducted with RNA transcripts of all six chimeric combinations of the 5' and 3' halves of the three satellite variants divided by a common restriction site, as well as with a mutated chimera. None of the chimeras containing the 5' half of Y induced lethal necrosis in tomato even when their 3' halves were that of the D variant with the conserved necrogenic element. Chimeras with the 3' half of Y elicited only partial or restricted necrosis which was much less severe than that induced by prototype variant D, and often was not lethal. Site-directed mutation of a single nucleotide in proximity to the necrogenic element of such a chimera containing the 3' half of Y restored much lethal necrogenicity. The results revealed the presence of structural elements in CMV satellite variant Y that modulate or even suppress the expression of the 3' conserved necrosis-determining element. They indicate that in CMV satellites widely separated sequence elements constituting a three-dimensional requirement are responsible for eliciting lethal necrosis in tomato.

Tomato necrosis and the 369 nucleotide Y satellite of cucumber mosaic virus: factors affecting satellite biological expression

“…The varying necrotic response of tomato to Y satellites of CMV therefore indicates that this satellite has a potential necrogenicity that can surface in the more sensitive Best of All tomato variety, but can be obscured in the less sensitive Rutgers variety. The notion of a potential necrogenicity of CMV-Y satellites which is structurally suppressed is corroborated by new evidence that shows that the absence of certain sequence elements in the 5' half of Y-CARNA 5 that are present in D-CARNA 5 and essential to necrogenicity prevent expression of the 3' half necrogenic determinant (Wu & Kaper, 1992).…”

“…The primary structure of gel-eluted Y-CARNA 5 was determined using dideoxynucleotide chain termination sequencing with synthetic primer d(GGGTCCTG) (Kaper et al, 1986); terminal sequences were determined by partial cleavage of end-labelled RNA as described by Kaper et al (1988). Full-length cDNA of Y-CARNA 5 was cloned in pPM1 (Wu & Kaper, 1992). The Y-satRNA cDNA clone in pUTll8GG-S was previously constructed and sequenced by Kuwata et al (1988).…”

“…A recent structural investigation of the Y satellite of CMV, the ability of which to elicit lethal necrosis in tomato having been in dispute (Takanami, 1981;Kaper et al, 1986), has shown that the presence of a massive insertion/deletion in its 5' half essentially prevents necrogenic expression of the 3' half necrogenic determinant. It was concluded that this 5' half insertion/ deletion may have replaced an element that is a necessary part of a three-dimensional structure needed by CMV satellites to induce lethal tomato necrosis (Wu & Kaper, 1992).…”

Characterisation of a satellite RNA of Cucumber mosaic virus that induces chlorosis in Capsicum annuum

“…It suggests that Interestingly, these larger satRNAs containing inserted sequences also were isolated from Asia. Various data support the influence of RNA secondary structure on the symptom induction in tobacco and tomato [12,18,[30][31][32][33]. The examination of putative secondary structures for PepYsatRNA and its mutants using mFOLD software reveals that there are no significant differences between the secondary structures predicted (data not shown).…”

Interfering Satellite RNAs of Bamboo mosaic virus

“…With CMV in tomato, C 215 , C 286 and A 330 of WLM2-satCMV could independently affect necrosis induction with different CMV strains (Wu and Kaper, 1992; Sleat et al, 1994), and the satCMV Y-strain nucleotide 185/186 caused yellow mosaic symptoms in tobacco (Jaegle et al, 1990). For the PSV system, U 226 and C 262 determine symptom attenuation of PSV G-satRNA in tobacco (Naidu et al, 1992).…”