A Single Nucleotide Change in the Coat Protein Gene of Tobacco Mosaic Virus Is Involved in the Induction of Severe Chlorosis

Abstract

YSI/1 is a mutant of the common strain (U1) of tobacco mosaic virus (TMV) which induces a severe yellow mosaic in Nicotiana tabacum instead of the light green/dark green mosaic induced by its parental U1 virus. Although there was less coat protein (CP) in whole leaf extracts of YSI/1-infected leaves than in U1-infected leaves, severalfold more CP was found in the chloroplasts, most of which was associated with the thylakoids. Sequencing the CP genes of both viruses showed the presence of nucleotide differences at viral RNA positions 5770 and 6127, both of which result in amino acid replacements; YSI/1 has an Asp-->Val change at amino acid 19 and a Ser-->Phe change at amino acid 138. A common strain TMV engineered to contain the YSI/1 3' end sequences, including the CP, induced the severe yellow mosaic of the YSI/1 mutant. A chimeric virus with the change only at nucleotide 5770 (amino acid 19) in the CP induced a severe yellow mosaic, showing that this replacement is involved in the induction of chlorosis by YSI/1. A second isolate of the same chimera also induced severe yellow mosaic symptoms; sequencing showed that it had gained the change at nucleotide 6127. However, a chimeric virus with the change only at nucleotide 6127 (amino acid 138) in the CP was unable to induce the severe yellow mosaic.

A cucumber mosaic virus mutant lacking the 2b counter-defence protein gene provides protection against wild-type strains

“…To exclude the possibility that Fny-CMVD2b triggers a general plant defence mechanism against all viruses, plants were challenged with an unrelated virus. TMV strain YSI/1 is a yellowing strain of TMV that induces strong, easily observable symptoms on tobacco (Banerjee et al, 1995). As expected, Fny-CMVD2b did not protect plants against challenge infection with TMV YSI/1 (Fig.…”

“…Experiments with TMV were carried out using xanthi, rather than xanthi-nc, which is resistant to this virus. The naturally occurring TMV mutant YSI/1 was used since it induces clearly observable yellow mosaic symptoms (Banerjee et al, 1995).…”

“…Experiments with TMV were carried out using xanthi, rather than xanthi-nc, which is resistant to this virus. The naturally occurring TMV mutant YSI/1 was used since it induces clearly observable yellow mosaic symptoms (Banerjee et al, 1995).Inoculation of plants and RNA extraction. For cross-protection experiments, tobacco and N. benthamiana plants at the three-to-four leaf stage were inoculated with Fny-CMVD2b virions suspended in water at a concentration of 100 mg ml 21 .…”

Virulence and molecular polymorphism of Prunus necrotic ringspot virus isolates.

“…However, the role of viral proteins in the elicitation of symptoms by other plant RNA viruses has been studied in some detail. For example, point mutations in the coat protein gene of tobacco mosaic virus have been shown to trigger a hypersensitive response in some Nicotiana species (Culver et al, 1994) or induce severe necrosis in others (Banerjee et al, 1995), although the viral replicase and movement protein genes also play roles in symptom expression (Holt et al, 1990). The expression level of 3a movement protein of tomato aspermy cucumovirus was found to be a determinant in symptom severity (Moreno et al, 1997).…”

Interaction of the Tobacco Mosaic Virus Replicase Protein with the Aux/IAA Protein PAP1/IAA26 Is Associated with Disease Development

“…Numerous changes in specific TMV genes have been identified as conferring either attenuated or severe disease symptoms (13). For example, amino acid substitutions in the coat protein have been linked to chlorosis, while specific mutations in the replicase protein can disrupt its function as an RNA silencing suppressor, resulting in reduced accumulation of virus and milder disease symptoms (3,10,16,35). However, the specific molecular mechanisms through which these TMV components affect the disease process remain unidentified.…”