Cucumber mosaic virus satellite RNA (Y strain): analysis of sequences which affect yellow mosaic symptoms on tobacco

Abstract

Plants infected with cucumber mosaic virus (CMV) (KIN strain) produce a mild mosaic disease on tobacco whereas infections of CMV with satellite RNA (strain Y) cause a severe yellow mosaic. Analysis of recombinant and mutant forms of satellite RNA identified a site (nucleotides 185/186) in the Y satellite RNA that affects the ability to induce the yellow mosaic in combination with CMV but not with tomato aspermy virus. The location of this site with respect to other mutations in the satellite RNA indicated that polypeptides, which may be encoded by the satellite RNA, have no role in induction of yellow mosaic symptoms. The symptom induction is therefore an effect of the satellite RNA on the host plant with the intervention of the helper virus. In the course of the mutation analysis of satellite RNA we detected several secondary mutations which arose in planta. Two of these were deletions of more than 80 nucleotides. Other forms of mutant satellite RNA were non-functional even though the modifications involved nucleotides completely within the large secondary deletions. These data imply complex intramolecular interactions in the satellite RNA.

Short Silencing RNA: The Dark Matter of Genetics?

“…If a virus-induced cascade targets mRNAs, there could be viral symptoms that are caused by silencing. There are several examples of viral or viroid RNAs that have properties predicted of silencing RNAs in that they induce symptoms but do not encode proteins (Devic et al 1989;Jaegle et al 1990;Wang et al 2004). However, there is no reason, in principle, that coding sequence viral RNAs could not also induce symptoms by silencing.…”

Trans-acting untranslated elements of groundnut rosette virus satellite RNA are involved in symptom production.

“…Although most CMV satRNAs attenuate the symptoms induced by CMV in all host species tested, some satellite isolates intensify symptoms in certain hosts, for example inducing chlorosis in tomato and tobacco (Palukaitis, 1988) or necrosis in tomato (Takanami, 1981 ;Sleat et al, 1994). Sequences in the sat-RNA that control the symptom intensification have been mapped to specific nucleotide residues, and it has been shown that a few nucleotide sequence changes can alter the host response (Palukaitis, 1988 ;Masuta & Takanami, 1989 ;Jaegle et al, 1990 ;Sleat & Palukaitis, 1990 ;Sleat et al, 1994 ;Zhang et al, 1994). Furthermore, identical sat-RNAs can have different effects on symptoms when associated with different helper virus strains (Roossinck et al, 1992).…”

A determinant of disease symptom severity is located in the 3'-terminal noncoding region of the RNA of a plant virus.

“…For example, symptoms in tomato aspermy virusinfected tobacco plants were greatly reduced by the presence ofthe satellite RNA of cucumber mosaic virus (CMV) but the amount of virus produced in the plants was not altered (23). Specific domains of nucleotides governing the induction of symptoms have been identified in satellite RNAs of CMV (24)(25)(26)(27). It has been proposed that these domains are defined by the presence or absence of particular types of secondary structure in the RNA molecule (24,26), although other reports indicate that the primary nucleotide sequence might also be important (27).…”