Gentian Kobu-sho-associated virus: a tentative, novel double-stranded RNA virus that is relevant to gentian Kobu-sho syndrome

A virus-like dsRNA of about 23 kbp was detected in gentian plants showing Kobu-sho syndrome including stunting, shortened internodes, and tumors on stems, nodes and roots. Nucleotide sequence analysis has suggested that this dsRNA is related to Pestivirus species but not to any other plant viruses. It was protected from externally added RNase, suggesting that the dsRNA is encapsidated. The dsRNA was co-extracted in a crude homogenate of glutaraldehyde-fixed tissue with the virus-like particles that have been associated previously with Kobu-sho syndrome in gentian (Usugi et al. Jpn J Phytopathol 76:21–24, 2010). The RNA sequence was detected in more than 99 % of Kobu-sho gentian individuals but in less than 20 % of apparently healthy gentian individuals from fields affected with Kobu-sho. Thus, we propose naming the virus Gentian Kobu-sho-associated virus.     

Plant viruses and viroids in Japan

Journal of General Plant Pathology - An increasing number of plant viruses and viroids have been reported from all over the world due largely to metavirogenomics approaches with technological...     

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

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.     

Improved method for in situ biolistic transformation to analyze barley–powdery mildew interactions

Although the use of stable transformants is indispensable to elucidate mechanisms underlying molecular plant–pathogen interactions, this approach remains difficult to apply to crops. Alternatively, biolistic transformation has often been used as a transient expression method in various plants. In this study, we developed a method for in situ biolistic transformation without separating leaves from barley seedlings by using a hand-held particle bombardment system because unwounded leaves are preferable for analyzing interactions between barley and Blumeria graminis f. sp. hordei which requires healthy living cells. As a result, we found that the infection rate in intact leaves was higher than in separated leaves and that the transformation efficiencies in leaves were higher when plants were grown in vermiculite rather than in culture soil. Furthermore, we determined the appropriate inoculation time after bombardment to analyze the incompatible interaction and successfully monitored the gradual occurrence of cell death over time. Our system was suitable for relatively long-term follow-up analysis of the fate of each single cell during plant–pathogen interactions.     

Identification and characterization of Lisianthus necrotic ringspot virus,a novel distinct tospovirus species causing necrotic disease of lisianthus (Eustoma grandiflorum)

In 2007, lisianthus (Eustoma grandiflorum) plants with necrotic ringspots on the leaves were found in Kochi Prefecture, Japan. Tospovirus-like spherical enveloped particles with ca. 160 nm in diameter were observed with electron microscopy. The complete nucleotide sequence of the S RNA segment of the virus was determined, and phylogenetic analysis using deduced amino acid sequences of the nucleocapsid protein and the nonstructural S protein indicated that the virus is phylogenetically distinct from any known tospovirus species. The results suggest that the virus is a new member of the genus Tospovirus, in the family Bunyaviridae. The virus is the fifth distinct tospovirus occurring naturally in lisianthus in Japan. The necrotic symptoms were reproduced on lisianthus seedlings after mechanical inoculation. The host range of the virus isolate on several test plants was also examined.     

Breakdown of plant virus resistance: can we predict and extend the durability of virus resistance?

Cultivars with introgressed natural resistance genes have been widely used for plant disease control, especially in the control of virus diseases, for which no effective chemical control agent is available. However, we often encounter virus mutants that break down or overcome the resistance. In this review, recent studies will be discussed with respect to breakdown of plant virus resistance.