Abstract
The 5' noncoding region (NCR) of grapevine chrome mosaic nepovirus (GCMV) was cloned in a viral vector derived from potato virus X (PVX). The recombinant virus obtained was inoculated to Nicotiana benthamiana, N. clevelandii, and N. tabacum plants. Infected plants developed necrotic symptoms in place of the vein clearing and mosaic typically observed after inoculation with PVX. Northern (RNA) blot analysis showed that the replication of PVX was not specifically altered by the presence of the GCMV 5' NCR. Inoculation of recombinant PVX harboring deleted forms of the GCMV 5' NCR showed that the three stem-loop structures at the 3' end of the 5' NCR (nucleotides 153 to 206) are dispensable for the induction of necrosis. Further deletion analysis indicated that neither the 5'-most 70 nucleotides of the 5' NCR nor the downstream region (nucleotides 71 to 217) alone is able to induce the necrotic symptoms. In the presence of both the sequence encoding the GCMV coat protein and the GCMV 3' NCR, the GCMV 5' NCR failed to induce necrosis in the PVX background. The mechanisms by which the expression of the 5' NCR might modify PVX symptoms are discussed.
Highlights
Santa Cruz and Baulcombe 1993), by the replicase gene of TMV in N. tabacum plants containing the N gene (Padgett and Beachy 1993) and by the movement protein gene of tomato mosaic virus in tomato plants harboring the Tm-2 or Tm-22 gene (Meshi et al 1989; Calder and Palukaitis 1992)
We report here that a recombinant potato virus X (PVX) containing the 5′ noncoding region (NCR) of grapevine chrome mosaic nepovirus (GCMV) RNA-2 induced severe necrotic symptoms on three Nicotiana spp. displaying only chlorotic mosaic when infected with wild-type PVX
The GCMV 5′ noncoding regions (5′ NCRs) in itself must be responsible for the necrotic reactions observed because (i) several independently constructed PVX vectors that contained this region (PVX:5′NCR, PVX:5′NCR∆, and a spontaneous deletion mutant from PVX:5′CPGC3′) displayed the same phenotype while the presence of a foreign sequence usually attenuated the symptoms induced by PVX (Chapman et al 1992; Hammond-Kosack et al 1995; this study), (ii) Northern blot analysis showed that the necrotic symptoms were not associated with an increase in PVX replication, and (iii) the depressed accumulation of PVX:5′NCR cannot be responsible for the necrotic reaction either since it was observed with PVX:spacer, a virus that does not induce necrosis
Summary
Santa Cruz and Baulcombe 1993), by the replicase gene of TMV in N. tabacum plants containing the N gene (Padgett and Beachy 1993) and by the movement protein gene of tomato mosaic virus in tomato plants harboring the Tm-2 or Tm-22 gene (Meshi et al 1989; Calder and Palukaitis 1992). In vitro translation experiments showed that these stem-loop structures are not involved in translation efficiency (Brault 1990) Because these structures are conserved in occurrence, number, sequence, and secondary structure among various nepoviruses and their two genomic RNAs (Le Gall et al 1995b), they may play an important role in the viral infection cycle or in host/virus interactions. We chose to use a plant viral vector derived from PVX (Fig. 2A; Chapman et al 1992) to express the GCMV 5′ NCR, devoid of any other GCMV sequence, in plants This PVX vector has already proved efficient for the study of different aspects of plant/pathogen interactions (Rommens et al 1995; Hammond-Kosack et al 1995; Scholthof et al 1995; Culver 1996; Joosten et al 1997). Because the 5′ NCR had the same effect on three different Nicotiana spp., we suggest that it does not act as a host range determinant in this genus
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
