# Plant virus

A plant virus is a virus (a nano-scale infectious agent without a cell membrane) that infects plants. (Up until the 1800s fungi were considered to be plants — now, the concept of "plant" excludes fungi, procaryotes, and the red and brown algae.)

## Quotes

* ... tobacco mosaic virus ... it's been used as a model for more than fifty years, and scientists throughout the world have used it for a variety of studies.
** Roger N. Beachy: (March 26, 2010)"Roger Beachy (Danforth Center) Part 1: Biology of Plant Virus Infection". iBiology, YouTube. (quote from 1:50 of 28:01 in video)
* The interest in plant virus evolution can be dated to the late 1920s, when it was shown that plant virus populations were genetically heterogeneous, and that their composition changed according to the experimental conditions. Many important ideas were generated prior to the era of molecular virology, such as the role of hostand vector-associated selection in virus evolution, and also that small populations, gene coadaptation and evolutionary trade-offs could limit the efficiency of selection. The analysis of viral genomes in the 1980s and 1990s established the quasispecieslike structure of their populations and allowed extensive analyses of the relationships among virus strains and species. The concept that virus populations had huge sizes and high rates of adaptive mutations became prevalent in this period, with selection mostly invoked as explaining observed patterns of population structure and evolution. In recent times virus evolution has been coming into line with evolutionary biology, and a more complex scenario has emerged.
** Fernando García-Arenal and Aurora Fraile: (2008). "Questions and Concepts in Plant Virus Evolution: a Historical Perspective": 1–14. DOI:10.1007/978-3-540-75763-4_1.
* Plants have been explored for many years as inexpensive and versatile platforms for the generation of vaccines and other biopharmaceuticals. Plant viruses have also been engineered to either express subunit vaccines or act as epitope presentation systems. Both icosahedral and helical, filamentous-shaped plant viruses have been used for these purposes. More recently, plant viruses have been utilized as nanoparticles to transport drugs and active molecules into cancer cells. The following review describes the use of both icosahedral and helical plant viruses in a variety of new functions against cancer.
** Kathleen Hefferon: (2018). "Repurposing Plant Virus Nanoparticles". Vaccines 6 (1): 11. ISSN 2076-393X. DOI:10.3390/vaccines6010011.
* The discovery of the first non-cellular infectious agent, later determined to be tobacco mosaic virus, paved the way for the field of virology. In the ensuing decades, research focused on discovering and eliminating viral threats to plant and animal health. However, recent conceptual and methodological revolutions have made it clear that viruses are not merely agents of destruction but essential components of global ecosystems. As plants make up over 80% of the biomass on Earth, plant viruses likely have a larger impact on ecosystem stability and function than viruses of other kingdoms. Besides preventing overgrowth of genetically homogeneous plant populations such as crop plants, some plant viruses might also promote the adaptation of their hosts to changing environments. However, estimates of the extent and frequencies of such mutualistic interactions remain controversial.
** Pierre Lefeuvre, Darren P. Martin, Santiago F. Elena, Dionne N. Shepherd, Philippe Roumagnac, and Arvind Varsani: (2019). "Evolution and ecology of plant viruses". Nature Reviews Microbiology 17 (10): 632-644. DOI:10.1038/s41579-019-0232-3.
* Persistent infection, wherein a pathogen is continually present in a host individual, is widespread in virus–host systems. However, little is known regarding how seasonal environments alter virus–host interaction during such metastability. We observed a lineage-to-lineage infection of the host plant Arabidopsis halleri with Turnip mosaic virus for 3 years without severe damage. Virus dynamics and virus–host interactions within hosts were highly season dependent. Virus accumulation in the newly formed leaves was temperature dependent and was suppressed during winter. Transcriptome analyses suggested that distinct defence mechanisms, i.e. salicylic acid (SA)-dependent resistance and RNA silencing, were predominant during spring and autumn, respectively. Transcriptomic difference between infected and uninfected plants other than defence genes appeared transiently only during autumn in upper leaves. However, the virus preserved in the lower leaves is transferred to the clonal offspring of the host plants during spring. In the linage-to-linage infection of the A. halleri–TuMV system, both host clonal reproduction and virus transmission into new clonal rosettes are secured during the winter–spring transition. How virus and host overwinter turned out to be critical for understanding a long-term virus–host interaction within hosts under temperate climates, and more generally, understanding seasonality provides new insight into ecology of plant viruses.
** Mie N. Honjo, Naoko Emura, Tetsuhiro Kawagoe, Jiro Sugisaka, Mari Kamitani, Atsushi J. Nagano, and Hiroshi Kudoh: (2020). "Seasonality of interactions between a plant virus and its host during persistent infection in a natural environment". The ISME journal 14 (2): 506-518. DOI:10.1038/s41396-019-0519-4.

## See also

* Plants