How to Various Pathogens Impact Their Host Plants

¶ … evolution of plant viruses. All five peer-reviewed articles are related because they all delve into the evolution of plant viruses.

Plant feeding by insect vectors can affect life cycle, population genetics and evolution of plan viruses, Gutierrez, et al., 2013. Plants use insects as the vectors for the spread of viruses. Insects historically go from one plant (host) to another; but recent evidence shows that viruses in plants, as they evolve, can actually have an influence "vector physiology and behavior" (Gutierrez, 2013). There is the possibility that insect "stresses" -- while feeding on plants -- may cause "major switches" in the way viruses evolve in plants (Gutierrez, 610).

The researchers found that "numerous plant viruses" can be and are transmitted by not just one insect, but by several insects. For example one species of aphids probes into a plant and another aphid species also makes "test probes"; this creates a "genetic bottleneck" (Gutierrez, 616). Researchers learned that by measuring those bottlenecks they can understand the insect feeding behaviors. Insects that colonize on a host plant for a long-term provide the best chances for transmission of viruses (to the next plant they visit). Results of this research show that: a) when it is beneficial for the parasite to kill the host, it can; and b) some viruses in plants perceive the presence of virus-carrying insects and " ... switch a major aspect of the life cycle" through "tissue tropism" to kill the host "rapidly" (Gutierrez, 620).

Biological and molecular events associated with simultaneous transmission of plant

Viruses by invertebrate and fungal vectors, Syller, 2014. Syller explains that plants are often infected with more than one virus which allows the vector to transmit more than one virus simultaneously to another plant. This, in turn, results in " ... multiple infections of new host plants," which greatly increases the possibility of diseases spreading (Syller, 417). Syller addresses multiple infections by aphids, whiteflies, leafhoppers, planthoppers, fungi and nematodes. One issue Syller seeks to address is how frequently do multiple viral infections occur in "arable weeds" and "crop plants"? (417).

Syller explains (referencing existing empirical studies) that an aphid can transmit a "non-circulative" virus almost as soon as it acquires that virus (no latent period is required). The virions (the infectious part of a virus) lock on to the aphid's epicuticle (outer layer of the exoskeleton) which lines the mouthparts of the insect. But the circulative virus require longer for the aphid to feed; the virions are in the aphid's body now, and the virus ends up in the insect's salivary glands before being introduced into plants (Syller, 419). Whiteflies, on the other hand, are not known to transmit multiple viruses as often as aphids, albeit whiteflies transmit "tomato chlorosis virus" (ToCV) and Tomato infectious chlorosis virus (TICV) simultaneously; and whiteflies are also known to simultaneously infect Tobacco leaf curl virus (TLCV) and Okra yellow vein mosaic virus (OYVMV) in pepper plants in Mexico, among the "most important horticultural plants in Mexico" (Syller, 422).

As for leafhoppers and planthoppers, they are not known for " ... simultaneous transmission of two viruses," but leafhoppers transmit 27 plant viruses and planthoppers transmit 18 viruses (Syller, 422). Nematodes, meanwhile, live in the soil and are not as easy to investigate; however, the transmission of two simultaneously infected viruses has not been documented. But "mixed infections of plants by fungus" are rare, Syller writes (424).

Exploiting Chinks in the Plant's Armor: Evolution and Emergence of Geminiviruses, Rojas, et al., 2005. The authors explain that DNA viruses have " ... acquired and evolved mechanisms to manipulate" the machinery needed for DNA replication (Rojas, 2015). Historically, most viruses that infect plants have used an RNA genome, which suggests that strict "constraints" were once imposed by plants on DNA viruses (Rojas, 361). Recently, geminiviruses have "circumvented these impediments" and hence geminiviruses cause "severe economic losses to agricultural production worldwide" (Rojas, 361). What the authors state is that biotechnology needs to intervene because antiviral defense systems in plants have broken down, allowing the evolution of infectious viral DNA. Given the geminiviruses' alliance with insect vectors, strategies for resistance need to be developed to lessen the "enormous, worldwide, economic impact" (Rojas, 384). Again, this research was based on referencing existing empirical studies.

Evolution: viruses are key players, Nature, Witzany, et al., 2014. This piece is not written in order to make discoveries, but rather to review research already existing. The article based on research positing that all evolutionary theory should include information on viruses. The evolution and development of all cellular organisms -- because of host DNA -- has been influenced by viruses. After all, the review reminds readers, viruses are " ... the most abundant genetic entities on the planet"; indeed, nearly all genomes of organisms that are made up of cells have within them "viral sequences, elements of which are now essential in gene regulation" (Witzany, 343).