Investigation of geminivirus infection mechanisms and virus-host factor interactions

The research presented in this dissertation involves the investigation of the functional and biological properties of the Bean dwarf mosaic virus (BDMV) movement-associated proteins and their interaction with host factors.BDMV encodes two viral movement-related proteins, NSP and MP these proteins coordinate the movement of the viral genome from the nucleus to the cytoplasm, and cell-to-cell across the cell wall, respectively. Here, several lines of evidence (i.e., gel overlay, co-immunoprecipitation and co-localization) are presented that the BDMV NSP and MP protein interact with histories. The interaction domains were mapped to the N-terminus tail domain of the histories. Together, these results suggest that histones, especially histone H3, may play a role in BDMV cell-to-cell movement.The BV1 gene of the bipartite begomovirus genome encodes a nuclear shuttle protein (NSP), which is also an avirulence determinant in common bean. The function of the NSPs of two bipartite begomoviruses, BDMV and Bean golden yellow mosaic virus (BGYMV), was investigated using a series of hybrid DNA-B components expressing chimeric BDMV/BGYMV NSPs, and in genotypes of the two major common bean gene pools: Andean (cv. Topcrop) and Middle American (cvs. Alpine and UI 114). BDMV DNA-A co-inoculated with hybrid HBDBG4 (BDMV DNA-B expressing the BGYMV BV1) and HBDBG9 (BDMV DNA-B expressing a chimeric NSP with the N-terminal 1-42 amino acids from BGYMV) overcame the BDMV resistance of cv. UI 114. This established that the BDMV NSP is an avirulence determinant in cv. UI 114, and mapped the domain involved in this response to the N-terminus. BDMV DNA-A co-inoculated with hybrid HBDBG10, expressing a chimeric NSP with amino acids 43-92 from BGYMV, was not infectious, revealing an essential virus-specific domain. The capsid protein (CP) also played a gene pool-specific role in viral infectivity. Redundancy of the CP and NSP, which are nuclear proteins involved directly or indirectly in viral movement, provides a masking effect that may allow the virus to avoid host defense responses.