Alternanthera mosaic virus – an alternative ‘model’ potexvirus of broad relevance

Authors: Hammond, John; KIM, IK-HYUN - Chungnam National University; LIM, HYOUN-SUB - Chungnam National University

Submitted to: Korean Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2017
Publication Date: 6/19/2017
Citation: Hammond, J., Kim, I., Lim, H. 2017. Alternanthera mosaic virus – and alternative ‘model’ potexvirus of broad relevance. Korean Journal of Agricultural Science. 44:145-180.
DOI: https://doi.org/10.7744/kjoas.20170016

Interpretive Summary: Plant viruses cause losses of both yield and quality in many crop plants, and are especially prevalent in vegetatively propagated crops, including many ornamental plants. A review of current knowledge of Alternanthera mosaic virus (AltMV) is presented; AltMV was first discovered in a weed species in Australia about 20 years ago, and is now known to naturally infect a wide range of taxonomically diverse species from at least 24 plant families, with plants from at least four more families infected experimentally. Many ornamental species are naturally infected, often developing prominent symptoms affecting quality and marketability. AltMV is a member of the genus Potexvirus, but differs from the type member, Potato virus X, and other well-characterized members of the genus in a number of important ways, including targeting of one viral protein to chloroplasts, and apparent use of the chloroplasts as the site for viral replication. Amino acid sequence differences between various proteins of distinct isolates of AltMV have been associated with symptom severity and ability to induce necrosis at low temperatures, and differential interactions with host proteins. Infectious cDNA clones of AltMV have been developed and utilized for either high level protein expression, or for Virus-Induced Gene Silencing, a technique useful for discovering plant gene function. AltMV is therefore proposed as an alternate model system for study of potexvirus biology, to gain greater understanding of common features and differences within this important genus of plant viruses. The information reviewed here will be of value to plant disease diagnosticians, regulatory officials, plant virologists, and to molecular biologists interested in the uses of plant viruses as tools for gene expression and analysis of gene function.

Technical Abstract: Alternanthera mosaic virus (AltMV) is a member of the genus Potexvirus which has been known for less than twenty years, but has already become widespread in many ornamental crops, and has been detected in Australasia, Europe, North and South America, and Asia. The natural host range to date includes species in at least twenty-four taxonomically diverse plant families, with species in at least four other families known to be infected experimentally. AltMV has been shown to differ from Potato virus X (PVX), the type member of the genus Potexvirus, in a number of ways, including the subcellular localization of the Triple Gene Block 3 (TGB3) protein, apparent absence of interactions between TGB3 and TGB2, and in targeting of TGB3 and replication to the chloroplasts. Differences between AltMV variants have allowed identification of viral determinants of pathogenicity, including symptom severity and induction of necrosis at low temperatures, and identification of residues involved in interactions with host proteins. Infectious clones of AltMV differing significantly in symptom severity and efficiency of RNA silencing suppression have been produced, suitable either for high level protein expression (with efficient RNA silencing suppression) or for Virus-Induced Gene Silencing (VIGS; with weaker RNA silencing suppression), demonstrating a range of utility not available with most other plant viral vectors. The difference in silencing suppression efficiency was shown to be due to a single amino acid residue substitution in TGB1, and to differences in subcellular localization of TGB1 to the nucleus and nucleolus. A novel bipartite delivery system has also been developed, as have versions of high level protein expression and VIGS vectors based on the Gateway cloning system. AltMV is therefore proposed as an alternate model system for examining the molecular biology of potexviruses in order to gain a more comprehensive understanding of the commonalities and differences between members of the genus, by comparison to other well-characterized potexviruses including PVX, White clover mosaic virus, and Bamboo mosaic virus. The current state of knowledge of AltMV biology, including host range, strain differentiation, host interactions, and utility as a plant viral vector for both protein expression and VIGS are summarized.