Affiliation:
1. Research Faculty of Agriculture, Hokkaido University , Sapporo, Japan
2. Faculty of Agriculture, Department of Agricultural and Environmental Sciences, University of Miyazaki , Miyazaki, Japan
Abstract
ABSTRACT
Host adaptation plays a crucial role in virus evolution and is a consequence of long-term interactions between virus and host in a complex arms race between host RNA silencing and viral RNA silencing suppressor (RSS) as counterdefense. Leek yellow stripe virus (LYSV), a potyvirus causing yield loss of garlic, infects several species of
Allium
plants. The unexpected discovery of an interspecific hybrid of garlic, leek, and great-headed (GH) garlic motivated us to explore the host-adaptive evolution of LYSV. Here, using Bayesian phylogenetic comparative methods and a functional assay of viral RSS activity, we show that the evolutionary context of LYSV has been shaped by the host adaptation of the virus during its coevolution with
Allium
plants. Our phylogenetic analysis revealed that LYSV isolates from leek and their taxonomic relatives (
Allium ampeloprasum
complex; AAC) formed a distinct monophyletic clade separate from garlic isolates and are likely to be uniquely adapted to AAC. Our comparative studies on viral accumulation indicated that LYSV accumulated at a low level in leek, whereas LYSVs were abundant in other
Allium
species such as garlic and its relatives. When RSS activity of the viral P1 and HC-Pro of leek LYSV isolate was analyzed, significant synergism in RSS activity between the two proteins was observed in leek but not in other species, suggesting that viral RSS activity may be important for the viral host-specific adaptation. We thus consider that LYSV may have undergone host-specific evolution at least in leek, which must be driven by speciation of its
Allium
hosts.
IMPORTANCE
Potyviruses are the most abundant plant RNA viruses and are extremely diversified in terms of their wide host range. Due to frequent host switching during their evolution, host-specific adaptation of potyviruses may have been shaped by numerous host factors. However, any critical determinants for viral host range remain largely unknown, possibly because of the repeated gain and loss of virus infectivity of plants. Leek yellow stripe virus (LYSV) is a species of the genus
Potyvirus
, which has a relatively narrow host range, generally limited to hosts in the genus
Allium
. Our investigations on leek and leek relatives (
Allium ampeloprasum
complex), which must have been generated through interspecies hybridization, revealed that LYSV accumulation remained low in leek as a result of viral host adaptation in competition with host resistance such as RNA silencing. This study presents LYSV as an ideal model to study the process of host-adaptive evolution and virus-host coevolution.
Funder
MEXT | Japan Society for the Promotion of Science
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Cell Biology,Microbiology (medical),Genetics,General Immunology and Microbiology,Ecology,Physiology