Natural isolates of Brome mosaic virus with the ability to move from cell to cell independently of coat protein.
Brome mosaic virus (BMV) requires encapsidation-competent coat protein (CP) for cell-to-cell movement and the 3a movement protein (MP) is involved in determining the CP requirement for BMV movement. However, these conclusions have been drawn by using BMV strain M1 (BMV-M1) and a related strain. Here, the ability of the MPs of five other natural BMV strains to mediate the movement of BMV-M1 in the absence of CP was tested. The MP of BMV M2 strain (BMV-M2) efficiently mediated the movement of CP-deficient BMV-M1 and the MPs of two other strains functioned similarly to some extent. Furthermore, BMV-M2 itself moved between cells independently of CP, demonstrating that BMV-M1 and -M2 use different movement modes. Reassortment between CP-deficient BMV-M1 and -M2 showed the involvement of RNA3 in determining the CP requirement for cell-to-cell movement and the involvement of RNAs 1 and 2 in movement efficiency and symptom induction in the absence of CP. Spontaneous BMV MP mutants generated in planta that exhibited CP-independent movement were also isolated and analysed. Comparison of the nucleotide differences of the MP genes of BMV-M1, the natural strains and mutants capable of CP-independent movement, together with further mutational analysis of BMV-M1 MP, revealed that single amino acid differences at the C terminus of MP are sufficient to alter the requirement for CP in the movement of BMV-M1. Based on these findings, a possible virus strategy in which a movement mode is selected in plant viruses to optimize viral infectivity in plants is discussed.
Takeda
Atsushi
A
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Nakamura
Wakako
W
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Sasaki
Nobumitsu
N
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Goto
Kaku
K
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Kaido
Masanori
M
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Okuno
Tetsuro
T
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Mise
Kazuyuki
K
Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
D001483:Base Sequence; D017795:Bromovirus / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity / Q000502:physiology*; D036022:Capsid Proteins / Q000378:metabolism*; D027465:Chenopodium quinoa / Q000821:virology; D015967:Gene Expression Regulation, Viral; D008969:Molecular Sequence Data; D009068:Movement; D009154:Mutation; D010935:Plant Diseases / Q000821:virology; D018515:Plant Leaves / Q000821:virology*; D053830:Plant Viral Movement Proteins; D017422:Sequence Analysis, DNA; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D036022:Capsid Proteins; D053830:Plant Viral Movement Proteins; D014764:Viral Proteins