Expression of a potyvirus non-structural protein in transgenic tobacco

Overexpression of a Grapevine Sucrose Transporter (VvSUC27) in Tobacco Improves Plant Growth Rate in the Presence of Sucrose In vitro

The import of sugar from source leaves and it further accumulation in grape berries are considerably high during ripening, and this process is mediated via sucrose transporters. In this study, a grape sucrose transporter (SUT) gene, VvSUC27, located at the plasma membrane, was transferred to tobacco (Nicotiana tabacum). The transformants were more sensitive to sucrose and showed more rapid development, especially roots, when cultured on MS agar medium containing sucrose, considering that the shoot/root dry weight ratio was only half that of the control. Moreover, all transformed plants exhibited light-colored leaves throughout their development, which indicated chlorosis and an associated reduction in photosynthesis. The total sugar content in the roots and stems of transformants was higher than that in control plants. No significant difference was observed in the leaves between the transformants and control plants. The levels of growth-promoting hormones were increased, and those of stress-mediating hormones were reduced in transgenic tobacco plants. The qRT-PCR analysis revealed that the expression of VvSUC27 was 1,000 times higher than that of the autologous tobacco sucrose transporter, which suggested that the markedly increased growth rate of transformants was because of the heterogeneously expressed gene. The transgenic tobacco plants showed resistance to abiotic stresses. Strikingly, the overexpression of VvSUC27 leaded to the up regulation of most reactive oxygen species scavengers and abscisic acid-related genes that might enable transgenic plants to overcome abiotic stress. Taken together, these results revealed an important role of VvSUC27 in plant growth and response to abiotic stresses, especially in the presence of sucrose in vitro.

The Potyviridae cylindrical inclusion helicase: a key multipartner and multifunctional protein

A unique feature shared by all plant viruses of the Potyviridae family is the induction of characteristic pinwheel-shaped inclusion bodies in the cytoplasm of infected cells. These cylindrical inclusions are composed of the viral-encoded cylindrical inclusion helicase (CI protein). Its helicase activity was characterized and its involvement in replication demonstrated through different reverse genetics approaches. In addition to replication, the CI protein is also involved in cell-to-cell and long-distance movements, possibly through interactions with the recently discovered viral P3N-PIPO protein. Studies over the past two decades demonstrate that the CI protein is present in several cellular compartments interacting with viral and plant protein partners likely involved in its various roles in different steps of viral infection. Furthermore, the CI protein acts as an avirulence factor in gene-for-gene interactions with dominant-resistance host genes and as a recessive-resistance overcoming factor. Although a significant amount of data concerning the potential functions and subcellular localization of this protein has been published, no synthetic review is available on this important multifunctional protein. In this review, we compile and integrate all information relevant to the current understanding of this viral protein structure and function and present a mode of action for CI, combining replication and movement.

Expression of Potato virus Y cytoplasmic inclusion protein in tobacco results in disorganization of parenchyma cells, distortion of epidermal cells, and induces mitochondrial and chloroplast abnormalities, formation of membrane whorls and atypical lipid accumulation

Infection of plant cells by potyviruses induces the formation of cytoplasmic inclusions ranging in size from 200 to 1000 nm. To determine if the ability to form these ordered, insoluble structures is intrinsic to the potyviral cytoplasmic inclusion protein, we have expressed the cytoplasmic inclusion protein from Potato virus Y in tobacco under the control of the chrysanthemum ribulose-1,5-bisphosphate carboxylase small subunit promoter, a highly active, green tissue promoter. No cytoplasmic inclusions were observed in the leaves of transgenic tobacco using transmission electron microscopy, despite being able to clearly visualize these inclusions in Potato virus Y infected tobacco leaves under the same conditions. However, we did observe a wide range of tissue and sub-cellular abnormalities associated with the expression of the Potato virus Y cytoplasmic inclusion protein. These changes included the disruption of normal cell morphology and organization in leaves, mitochondrial and chloroplast internal reorganization, and the formation of atypical lipid accumulations. Despite these significant structural changes, however, transgenic tobacco plants were viable and the results are discussed in the context of potyviral cytoplasmic inclusion protein function.

Nicotiana benthamiana plants transformed with the plum pox virus helicase gene are resistant to virus infection

Nicotiana benthamiana Domin. plants were transformed with the cytoplasmic inclusion protein (CI) gene of plum pox potyvirus (PPV) to investigate, whether this non-structural protein would be able to confer resistance. The CI protein is an RNA helicase, which contains a conserved nucleotide binding motif (NTBM) and plays an important role in viral replication. Two gene constructions were developed for plant transformation. The first contains the original coding sequence of the CI gene under the control of 35S-promoter and nos terminator signal, the second is mutated in the NTBM region. Several transgenic plant lines were obtained following Agrobacterium tumefaciens-mediated transformation. The integration of the viral genes into the plant genome was confirmed using the polymerase chain reaction and the transgene derived mRNAs were detected by Northern blot hybridization. The CI protein in the transgenic plants could not be detected by Western blot analyses. One transgenic line containing the mutated CI gene remained completely symptomless after PPV infection, indicating that the putative defective helicase gene was capable of eliciting virus resistance.

5' proximal potyviral sequences mediate potato virus X/potyviral synergistic disease in transgenic tobacco

The interaction of potato virus X (PVX) and potato virus Y (PVY) in tobacco causes a synergistic disease characterized by a dramatic increase in symptom severity, a change in the regulation of PVX RNA replication, and an increase in accumulation of PVX. In this study we demonstrate that PVX also interacts synergistically with three other members of the potyvirus group of plant viruses, tobacco vein mottling virus (TVMV), tobacco etch virus (TEV), and pepper mottle virus. These synergisms resemble the classic PVX/PVY synergism with respect to both the increase in host response and the change in PVX replication. To determine if the induction of PVX/potyviral synergism requires potyviral genome replication per se or if the response is mediated by expression of one or more potyviral genes, we used tobacco plants stably transformed with various subsets of the TVMV genome. PVX infections of transgenic plants expressing the 5'-proximal region of the TVMV genome, including the protease-1, helper component protease, and protein-3 genes, result in symptoms resembling those of PVX/potyviral synergism. A similar synergistic-like response occurs when transgenic tobacco plants expressing the analogous but smaller region from the 5'-proximal region of the TEV genome were infected with PVX. Replication of PVX RNA is altered in transgenic plants expressing 5'-proximal sequences of either TVMV or TEV, and in a manner similar to that observed in double infections. These results indicate that replication of the potyviral genome is not required for PVX/potyviral synergism and that the response is mediated by expression of potyviral sequences which have been localized to the 5'-proximal third of the genomic RNAs of both TVMV and TEV.

Serological relationships involving potyviral nonstructural proteins

This report represents a compilation of many of the publications on antigenic properties of potyviral-specified nonstructural proteins. Polyclonal antisera have been prepared for use in characterization of six nonstructural proteins. These include antisera to the cylindrical inclusion proteins of at least 28 potyviruses, to small nuclear inclusion protein (protease) of four potyviruses, to large nuclear inclusion protein (putative replicase) of three viruses, helper component-protease or amorphous inclusion protein of at least four viruses, to the P1 protein (located at the N-terminus of the polyprotein) of one virus, and to the P3 protein (located between helper component protease and cylindrical inclusion protein) of one virus. Monoclonal antibodies also have been prepared to several of these nonstructural proteins. The evidence thus far indicates that cylindrical inclusions of different potyviruses have both conserved and unique epitopes. Nuclear inclusion proteins and amorphous inclusion proteins also may have conserved and unique epitopes. Antigenic relationships of potyviral nonstructural proteins have potential for the identification and classification of potyviruses.