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  • Brin Oneill posted an update 1 week, 1 day ago

    Plants, insects and viruses: intimate relationshipsOther than through seed dispersal most plants do not move across significant distances; hence their horizontally-transmitted viruses must be moved by others. Most often the vectors for plant viruses are insects, although below ground transmission also occurs through nematodes, chytrids or plasmodiophorids. The relationships among plants, insects and viruses are ancient, and it is not surprising that they are intimate and complex. Insects vectors are in turn colonized by other entities, and endosymbiotic bacteria produce compounds that are involved in plant virus transmission as well (Morin et al., 1999; vandenHeuvel et al., 1994). Although similar relationships with other vectors exist, they are less well studied and will not be considered here.Insect transmission of plant viruses is usually categorized in four ways (Table 1), depending on how long the insect needs to feed to acquire the virus, how long it remains viruliferous, how long it must feed to transmit the virus, and whether or not the virus circulates through the insect gut and/or propagates in the insect [comprehensively reviewed in Bragard et al. (2013)]. These transmission modes affect the evolution of plant–virus–insect relationships.Viruses and host evolutionThe role of viruses in the evolution of life has been explored in depth in many recent publications (Forterre and Prangishvili, 2013; Koonin and Dolja, 2014; Villarreal and Ryan, 2011; Villarreal, 2005; Villarreal and Witzany, 2010). In addition to the ancient relationships between viruses and hosts that have molded aspects of host immunity and response to viruses, the number of virus-like sequences found in eukaryotic genomes reveals the existence of other ancient relationships that are, as yet, not understood. Here I will provide a few highlights of recent data from plant viruses.Ecologists have done extensive studies on genotype versus environment, or G X E effects, and although disease has been thought to be important in the genotype diversity, the evidence for this minimal. One study using White clover mosaic virus (WClMV) on a variety of white clover genotypes found that the virus had a negative impact on all genotypes but the degree of impact varied greatly from one genotype to another, providing empirical evidence that a virus in the environment can effect the genotypic Cyclo or G X E (vanMölken and Stuefer, 2011). Hence while host diversity can impact the incidence and outcome of virus infection in plants (Roossinck and García-Arenal, 2015), viruses also can impact the degree of host diversity.Viral impacts on plant ecologyConclusionsAcknowledgmentsThe author acknowledges support from the Pennsylvania State University College of Agricultural Science, by the National Science Foundation Grant numbers EF-0627108, EPS-0447262, IOS-0950579, and IOS-1157148, and the United States Department of Agriculture Grant number OKLR-2007-01012.IntroductionThere are more than 2000 virus species and those affecting plants include viruses of at least 21 families and 8 unassigned genera, many of which cause important diseases of various plants that humans grow for food and/or fiber (Hull, 2014). In addition, many plant viruses have been found associated with non-cultivated plants, and new plant viruses are being discovered every day. Virus diseases make up 47% of the new emerging diseases affecting plants (Anderson et al., 2004). Thus, plant infecting viruses are very successful. As virus hosts, plants differ from animals and even bacteria in several ways, but one that is critical in terms of virus biology is that plants are sessile. In order to survive, plant-infecting viruses must have an efficient means to move from one plant host to another. To do so, the great majority of plant viruses utilize specific vectors to ensure their ability to move from one plant to another, and to ensure their survival, plant viruses encode for specific proteins that facilitate this process (Table 1) (Kritzman et al., 2002; Moreno et al., 2012; Moritz et al., 2004). Although there are different types of plant-associated organisms including fungi, nematodes and various types of invertebrates that serve as vectors for different plant viruses, the majority of plant viruses utilize specific plant feeding insects as their primary vector(s), and here we focus on insect-transmitted plant viruses. Proteins encoded by different plant viruses have been identified to specifically interact with their respective insect vectors and facilitate virus transmission, and there are many excellent papers and reviews on these subjects (Ammar et al., 2009; Hogenhout et al., 2008; Ng and Falk, 2006). However, recent studies suggest additional complexities for plant virus:vector relationships (Blanc et al., 2014; Gutierrez et al., 2013). Here we discuss the current state of this knowledge, but also recent exciting translational applications of fundamental knowledge of virus:insect vector interactions that has opened up new doors for plant virus and insect vector control.