Cellular Functions of the Squash Leaf Curl Geminivirus Movement Proteins BL1 and BR1
Ward, Brian Michael
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Permalink
https://hdl.handle.net/2142/86741
Description
Title
Cellular Functions of the Squash Leaf Curl Geminivirus Movement Proteins BL1 and BR1
Author(s)
Ward, Brian Michael
Issue Date
1998
Doctoral Committee Chair(s)
Lazarowitz, Sondra G.
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
Plant viruses encode what are typically called movement proteins (MPs). These are defined as proteins dispensable for viral replication and encapsidation, but essential for cell to cell movement of the virus to the phloem and eventually leading to systemic infection of the plant. Unlike most plant viruses squash leaf curl geminivirus (SqLCV) encodes two movement proteins termed BR1 and BL1. This is most likely due to the fact that SqLCV is a ssDNA virus and must replicate in the nucleus, therefore, SqLCV not only needs to cross the cell wall like other cytoplasmically replicating plant viruses, but must get out of the nucleus to do so. Previous studies in our lab have defined several functions for the two movement proteins. BR1 is an ssDNA binding protein that localizes to the nuclei of infected cells and functions as a nuclear shuttle protein. BL1 is directly responsible for viral pathogenic properties, and transient expression assays in tobacco protoplasts demonstrated that BL1 provides directionality to virus movement by cooperatively interacting with BR1 to redirect it from the nucleus to the cell periphery. In this work I immunolocalize BL1 to unique 37 nm wide tubules in phloem parenchyma cells from infected pumpkin plants. I further demonstrate that these tubules are derived from the endoplasmic reticulum. Separately, I demonstrate the BR1 contains a functional leucine-rich nuclear export sequence (NES). This NES is contained between residues 184--193 of BR1 and is the first report of nuclear export in plants. Further, I show that the BL1 interactive domain on BR1 is entirely contained within the COOH-terminal 57 amino acids and is separate from the NES. This work provides an in vivo assay for looking at nuclear export in plants.
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