|Van Winkle, David|
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 2010
Publication Date: January 20, 2011
Repository URL: http://hdl.handle.net/10113/49437
Citation: Tatineni, S., Van Winkle, D.H., French, R.C. 2011. The N-terminal region of Wheat streak mosaic virus coat protein is a host- and strain-specific long-distance transport factor. Journal of Virology. 85: 1718-1731. Interpretive Summary: Wheat streak mosaic virus isolates, Sidney (WSMV-S) and Type (WSMV-T), share 98.7% polyprotein sequence identity but differentially infect Zea mays inbred line SDp2: WSMV-S induces a systemic infection but WSMV-T does not. Co- and sequential-inoculation of SDp2 with WSMV-S and/or WSMV-T did not prevent systemic infection of SDp2 by WSMV-S, suggesting that WSMV-T does not induce a defense response to restrict the virus to inoculated leaves. By making sequence/gene exchanges between WSMV-T and WSMV-S and by site-directed mutagenesis, we have identified four specific amino acids at the N-terminus of viral coat protein (CP) that enable the virus to infect SDp2 systemically. We found resistance of SDp2 to WSMV-T infection was due to a block in long-distance movement of the virus but not due to defects in replication or cell-to-cell movement. Our results suggest that the four differing amino acids at the N-terminal region of CP between WSMV-S and WSMV-T isolates probably are crucial for interactions with SDp2 proteins for efficient long-distance movement. In the absence of such compatible interactions between the CP and host proteins, virions either inefficiently enter into and/or are transported through the phloem. Taken together, we found that the N-terminal region of CP functions in host- and strain-specific long-distance transport of WSMV.
Technical Abstract: Understanding the genetics underlying host range differences among plant virus strains can often provide valuable insights into viral gene functions and virus-host interactions. In this study we examined viral determinants and mechanistics of differential infection of Zea mays inbred line SDp2 by Wheat streak mosaic virus (WSMV) isolates. WSMV isolates Sidney 81 (WSMV-S) and Type (WSMV-T) share 98.7% polyprotein sequence identity but differentially infect SDp2: WSMV-S induces a systemic infection but WSMV-T does not. Co- and sequential-inoculation of SDp2 with WSMV-T and/or WSMV-S did not affect systemic infection by WSMV-S, suggesting that WSMV-T does not induce a restrictive defense response but that viral-encoded proteins may be involved in differential infection of SDp2. The viral determinant responsible for strain-specific host range was mapped to the N-terminus of coat protein (CP) by systematic exchanges of WSMV-T sequences into that of WSMV-S and by reciprocal exchanges of CP or CP amino acids 1 to 74. GFP-tagged WSMV-S with CP or CP residues 1 to 74 from WSMV-T produced similar numbers of infection foci and genomic RNAs in inoculated leaves as with WSMV-S, indicating that failure to infect SDp2 systemically is not due to defects in replication or cell-to-cell movement. However, these GFP-tagged hybrids showed profound defects in long-distance transport of virus through the phloem. Furthermore, we found four of the five differing amino acids in the N-terminus of CP between WSMV-S and WSMV-T isolates were collectively involved in systemic infection of SDp2. Taken together, these results demonstrate that the N-terminal region of tritimoviral CP functions in host- and strain-specific long-distance movement.