Partial purification of inclusions induced by tobacco etch virus and potato virus Y

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.

Serological relationships between the cylindrical inclusion proteins of potyviruses

ABSTRACT Antisera to the cytoplasmic inclusion proteins (CIPs) of bean yellow mosaic (BYMV), clover yellow vein (ClYVV), turnip mosaic (TuMV), sweet potato feathery mottle (SPFMV), and maize dwarf mosaic (MDMV) potyviruses were used to examine the relationships between the CIPs of 18 potyviruses. The antisera to CIPs of BYMV, ClYVV, TuMV, and SPFMV cross-reacted to most or all of the purified CIPs tested in western blot assays. The MDMV CIP antiserum reacted significantly only to the MDMV and sorghum mosaic virus CIPs. Reactivity of antisera to CIPs of dicot-infecting viruses was generally higher with CIPs of other dicot-infecting than with monocot-infecting potyvirus CIPs. Analysis of amino acid sequences of the CI genes of 11 well-characterized potyviruses suggested that epitopes specific for individual potyviruses are primarily in the C-terminal domains of the CIP, whereas epitopes shared among different viruses are clustered in the N-terminal domains. The most highly conserved predicted epitope overlaps the nucleotide binding motif of the N-terminal helicase domain of the CIP. Antibodies to this domain will probably be present in antisera to any potyvirus CIP and contribute to the cross-reactivity observed. Differences in the C-terminal domains may correlate with interactions between the CIP and coat protein necessary for replication and movement.

Sequence and phylogenetic analysis of the cytoplasmic inclusion protein gene of zucchini yellow mosaic potyvirus: its role in classification of the Potyviridae

The cytoplasmic inclusion (CI) gene of a Singapore isolate of zucchini yellow mosaic virus (ZYMV-S) was sequenced and compared with CI of 14 other potyviruses. In addition to the consensus sequence GAVGSGKST of nucleotide binding motif (NTBM) which is implicated as a membrane-binding component of the RNA helicase complex, five other conserved motifs were found. Phylogenetic trees were constructed from sequence data for the CI and the coat protein. Similar branching patterns obtained from both CI and coat protein analyses suggests that phylogenetic relationship among potyviruses can be determined using the CI. We propose that phylogenetic analysis of CI gene may be used as an alternative approach for the study of evolution within the family Potyviridae.

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.

An improved purification procedure for preparing potyviruses and cytoplasmic inclusions from the same tissue

Twelve different potyviruses and cytoplasmic inclusion proteins were purified from a range of plant species utilizing a single purification protocol. Highly purified preparations have been obtained with yields that reflect the relative concentrations in the starting material; virus yields of up to 15 mg per 100 g of tissue were obtained. In some cases aggregation resulted in losses of significant amounts of virus to the inclusion fraction; this varied among preparations of the same virus. Preparations obtained from cesium gradients were typically unaggregated and essentially free of host materials. Purified virus was suitable for the production of antisera with high specific titers and low titers against healthy plant antigens. Both purified virus and RNA prepared from the virus retained infectivity. Purified RNA was free of detectable host plant nucleic acids, as complementary DNA preparations synthesized using virion RNA as template were highly virus-specific.

Pinwheel inclusions in morphogenesis: a possible alternative to induction by viruses

Pinwheel inclusions (PWs) were found in cells of callus tissue derived from explants of secondary phloem parenchyma of carrot (Daucus carota) storage root and grown on a basal medium containing zeatin and indoleacetic acid or coconut milk, naphthalene acetic acid, or combinations of these. Preliminary attempts to demonstrate the presence of viruses in the callus tissue failed. The possibility that the tissles were infected by a low titer or unstable conventional virus or by a defective mutant has not been ruled out. However, two lines of evidence suggest that the PWs in these tissues may be a result of culture conditions and not of virus infection. First, no PWs or other cytoplasmic inclusions were found in cells of otherwise similar tissue cultured on basal medium alone, and multifibrillar bundles (MFBs) but not PWs were found when the tissues were cultured on a medium that stimulates differentiation and morphogenesis. Second, culture stimulated to differentiate and containing MFBs only were returned to the supplemented basal medium and subsequently found to contain both PWs and MFBs.