Keeping up With Virus Taxonomy: Viruses that infect plants
Posted on April 5, 2024 by Clare Baker
Welcome back to Keeping up with Virus Taxonomy. In previous editions, we’ve looked at viruses that infect bacteria, fungi and humans so it’s about time that we take a look at virus families that infect plants.
Potyviridae
Our first family is Potyviridae, a family of monopartite and bipartite plant viruses. Monopartite refers to viruses which have a single molecule of nucleic acid and bipartite refers to instances in which the genome is divided into two or more segments. Potyvirids are vectored by a variety of organisms, seeds or pollen. Members of the genera Potyvirus and Macluravirus are transmitted by aphids, the most common vector of plant viruses. However, the vectors of other members of the family including rose yellow mosaic virus and the two known arepaviruses remain unknown.
Geminiviridae
Next up we have Geminiviridae, a family of small, non-enveloped viruses with genomes comprising of one or two single-stranded circular DNAs. The family is diverse, and viruses classified into the 14 genera show distinct host ranges, insect vectors and genome organisations. Unsurprisingly, this diverse family infect a wide range of plant species and are transmitted by various insects including whiteflies, leafhoppers, treehoppers and of course, aphids. Geminiviruses are important plant pathogens which cause economically important diseases in most tropical and subtropical regions of the world. However, when looking at a genus in the family - begomoviruses - geographical clusters are apparent. This possibly reflects their evolutionary divergence as a consequence of isolation as their vectors cannot fly long distances. It is remarkable that this remains the case despite the increasing global movement of plants and inter-species recombination events.
Alphaflexiviridae
Alphaflexiviridae are a family of viruses which infect plants and plant-infecting fungi. A typical member of this family is the little-known shallot virus X from the genus Allexivirus. Many of the viruses within this family have relatively mild effects on their host. Alphaflexiviruses have been reported to infect a wide range of plant species but the host range of individual species within this family are usually limited.
Caulimoviridae
This family includes non-enveloped, reverse-transcribing plant viruses of which a typical member is the cauliflower mosaic virus. Much like other members on this list, members of Caulimoviridae infect economically important crops. Many members of the family are spread by vegetative propagation, where a new plant grows from a cutting of a single plant. While this is a cost-efficient way of growing plants, it enables viruses such as those in the Caulimoviridae family to perpetuate1.
Bromoviridae
Finally, we have the family Bromoviridae. This family earns its name from the brome mosaic virus which belongs to the genus Bromovirus. The brome mosaic virus infects cereal plants causing mosaic symptoms2 – yellow, white or green stripes, streaks or spots on parts of the plant. Many viruses in this family infect economically important crops including cucumber, cereal, olive and tobacco plants3.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for developing and maintaining a universal virus taxonomy. Known viruses are categorised into a classification scheme taking into consideration their physical and biological properties in combination with their phylogenetic relationships.
These two-page summaries of each chapter of the ICTV Report (a free resource published by the ICTV which provides an up-to-date description of virus taxonomy) are freely available in the Journal of General Virology, and are supported by the Microbiology Society. These summaries are known as ICTV Virus Taxonomy Profiles and describe the structure, replication and taxonomy of each virus order and family.
References
1Roger Hull, in Matthews' Plant Virology (Fourth Edition), 2002
2 X. Wang, P. Ahlquist, in Encyclopedia of Virology (Third Edition), 2008
