Attenuated plant viruses: preventing virus diseases and understanding the molecular mechanism

Abstract

Attenuated viruses have been isolated and studied not only as a practical means of controlling virus diseases but also to gain a molecular understanding of viral virulence and cross protection. They have been isolated from crop fields and generated through high/low temperature treatment or by mutagens such as nitrous acid and ultraviolet irradiation. Some viruses have been beneficially used in fields and evaluated for one or more decades. Molecular genetic studies on attenuated viruses have revealed that amino acid substitutions are located in replicase and the movement protein in tobamovirus, protein 2b for cucumovirus, and P1 and HC-Pro for potyvirus. In most cases, with a few exceptions, symptom attenuation is positively correlated with a reduced level of RNA silencing suppression. Molecular mechanisms underlying virus attenuation and cross protection and the rationale for practical use of attenuated viruses for effective virus disease control are discussed.

Molecular analysis of an attenuated strain of Cucumber green mottle mosaic virus using in vitro infectious cDNA clone: pathogenicity and suppression of RNA silencing

“…Alignment of the amino acid sequences of CGMMV-SH and CGMMV-SH33b revealed that five amino acid substitutions were found between the two virus strains: Gly at amino acid residue 480, Val at 1124, Asp at 1157 and Ser at 1397 of RP, and Val at 156 of CP for Glu, Ala, Asn, Pro and Ala in CGMMV-SH, respectively (Tan et al 1997). Although different tobamoviruses are known to be attenuated by the mutations in the replicase gene, none of the mutations are commonly found in different tobamoviruses (Nishiguchi and Kobayashi 2011).…”

“…This phenomenon has been successfully used to protect crops against severe viruses in tomato, melon and pepper plants in Japan (Nishiguchi and Kobayashi 2011). The phenomenon is virus specific and it works only between strains of the same virus and related virus species.…”

“…Measures to protect crops against virus infections include eradicating infected plants, using virus-free seeds and vegetative stocks, propagating and maintaining virus-free stocks, modifying planting and harvesting procedures, using resistant varieties and controlling virus vectors by insecticides and so on (Hull 2002). In addition to these, two important techniques employed for managing plant virus diseases includes cross protection using attenuated/mild strains (Nishiguchi and Kobayashi 2011) and transgenic or engineered resistance (Fuchs 2008). To elucidate the molecular basis for effective virus disease control by attenuated/mild strains or viruses, we analyzed pathogenicity, virus accumulation and suppression activity of RNA silencing of an attenuated strain of CGMMV.…”

Generation of an Attenuated, Cross-Protective Pepino mosaic virus Variant Through Alignment-Guided Mutagenesis of the Viral Capsid Protein

“…It was first reported by McKinney, who observed that tobacco plants preinfected with a mild variant of Tobacco mosaic virus (TMV) were protected from infections by a severe TMV strain (21,37). Similar observations have since been made with many other viruses, leading to the adoption of cross-protection to control viruses such as Citrus tristeza virus, Papaya rinspot virus, Zucchini yellow mosaic virus (ZYMV), and Potato virus X (PVX) (4,5,24,32,34).…”

Control of Cucurbit Viruses

“…Mild strains may be obtained either as natural occurring variants (as ZYMV-WK) or after various treatments including high or low temperature, nitrous acid, or UV irradiation treatments (Fuchs, Ferreira, et al, 1997;Lecoq, 1998;Nischiguchi & Kobayashi, 2011). After a combination of these treatments, mild strains of CMV, CGMMV, PRSV, WMV, and ZYMV have been obtained and tested under field conditions.…”