Name: Keizo Nagasaki

Email: nagasaki@affrc.go.jp

Author: Keizo Nagasaki1*, Hisae Kawami1, Hiroyuki Mizumoto1,2, Yuji Tomaru1

Author affiliation: 1) National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Hiroshima, Japan; 2) Present affiliation: Laboratory of Plant Pathology and Biotechnology, Faculty of Agriculture, Kochi University, Kochi, Japan

Abstract title: Algal virus variation vs. Algal host variation

Absstract:

HcRNAV is a polyhedral virus (T=3) infecting the bivalve-killing bloom-forming dinoflagellate Heterocapsa circularisquama. It harbors a linear 4.4-kb ssRNA genome in which two open reading frames (a replicase gene and a structural gene) were identified. In the RdRp sequence tree, this virus fell into a phylogenetic clade which is far distant from any other viruses ever known. The HcRNAV population was considered to be composed of multiple (at least 3) types which differ in intraspecies host specificity; i.e., these HcRNAV types differ in strain-specific infectivity among them. Results of genome comparison and protein tertiary structure prediction supported the hypothesis that the nanostructural difference on the viral surface among these virus types is crucial for determining the intraspecies infection specificity; i.e., some specific amino acid residues exposed to the virion surface tend to be different among virus clones having distinctive host ranges. Our prediction is that the type variations of H. circularisquama and its viruses are so large in natural environments; consequently, the host-virus relationship may be much more complicated than previously assumed.