![]() ![]() RNA3 also encodes two proteins, the 3a protein (movement protein MP) and the coat protein (CP), which are essential for virus movement and transmission. RNA2 also encodes the 2b protein, which has RNA silencing suppressor activity. ![]() The 1a and 2a proteins, along with some host factors, comprise the replicase complex. RNA2 encodes the 2a protein, which contains a viral RNA-dependent RNA polymerase (RdRp) domain. RNA1 encodes the 1a protein, which contains two functional domains: an N-terminal methyltransferase domain and a C-terminal helicase domain. The CMV genome is divided into three single-stranded RNAs, designated RNA1, RNA2, and RNA3 ( Palukaitis and Garcia-Arenal 2003 Jacquemond 2012). CMV isolates can also be classified into different pathotypes based on their virulence in specific plant species and varieties ( Lin et al. ![]() CMV isolates can be divided into three major subgroups (IA, IB, and II), based on their serological and molecular characteristics ( Roossinck 2002 Jacquemond 2012). 2014), suggesting the possibility of the host-adaptive evolution of CMV in pepper. In particular, a previous study showed that CMV populations infecting pepper display unique patterns of evolution in Korea ( Kim et al. Thus far, complete genome sequences of more than 110 CMV isolates have been reported, and extensive analyses of CMV population genetics have been performed to examine the evolutionary history of the virus ( Roossinck 2002 Kim et al. In over 100 years since its discovery ( Doolittle 1916 Jagger 1916), numerous CMV strains and isolates have been identified from various plant species, including dicots and monocots ( Jacquemond 2012). CMV has evolved to infect more than 1,200 species, comprising more than eighty plant families and has been dispersed worldwide ( Palukaitis and Garcia-Arenal 2003). However, mechanistic links between diversity, virulence, and in vivo selective pressures are little understood in the crop fields.Ĭucumber mosaic virus (CMV genus Cucumovirus, family Bromoviridae) is one of the most successful RNA viruses for host adaptation and dispersion. In this sense, the widespread use of resistant cultivars may apply significant selective pressures to direct the adaptive virulence evolution of viruses in crop fields ( Garcia-Andres et al. RNA viruses, the largest group of plant viruses, are known to have a rapid evolutionary rate due to error-prone replication and short generation times, allowing for fast virulence changes to sustain infection ( Cabanillas et al. Since viruses are obligate intracellular parasites and depend on their hosts for most aspects of the life cycle, they have thus evolved under host-interactive constraints ( Roossinck 2003 Lauring et al. IntroductionĪnalyzing the genetic diversity and population structure of a virus is an essential approach for understanding its evolutionary history and related mechanisms that drive its evolution and dispersion. Therefore, deployment of a single resistance gene may reduce resistance durability against CMV and more integrated approaches are warranted for successful control of CMV in pepper.Ĭucumber mosaic virus, RNA virus, evolution, resistance-breaking, pepper 1. Our findings suggest that resistance-driven selective pressures on RNA1 might have contributed in shaping the unique evolutionary pattern of CMV in pepper. We also demonstrated that nonsynonymous mutations in RNA1 encoding the 1a protein enabled CMV to overcome the deployed resistance in pepper. ![]() Our population genetics analysis revealed that the high divergence capacity of CMV RNA1 might have played an essential role in the host-interactive evolution of CMV and in shaping the CMV population structure in pepper. In this study, we examined the molecular and evolutionary characteristics of recently emerged, resistance-breaking CMV variants infecting pepper. Cucumber mosaic virus (CMV), a plant RNA virus with high evolutionary capacity, has caused endemic disease in various crops worldwide, including pepper ( Capsicum annuum L.), because of frequent emergence of resistance-breaking variants. While the deployment of host resistance in crops is the most efficient means to control various viruses, host resistance itself can act as strong selective pressure and thus play a critical role in the evolution of virus virulence. Understanding the evolutionary history of a virus and the mechanisms influencing the direction of its evolution is essential for the development of more durable strategies to control the virus in crop fields. ![]()
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