Masters Theses

Date of Award

12-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Life Sciences

Major Professor

David Hacker

Abstract

The southern bean mosaic virus (SBMV), the type member of the sobemovirus genus, is a positive sense icosohedral plant virus that systemically infects cowpea. Recently, it was determined that the p21 (ORF1) protein, p24 (ORF3) protein, and the CP were required for cell-to-cell movement of SBMV-C in cowpea. It is possible that these proteins are viral movement proteins, that is, they provide some function in viral movement. The goal of this study was to determine the subcellular localization of these three viral proteins and begin to elucidate their roles in cell-to-cell and/or long distance movement. Previously, the movement characteristics of this virus were unknown. Using immunocytochemistry, virus was found to localize in the xylem and phloem of infected cowpea, although most plant viruses traffic only in the phloem.

Cell-to-cell movement of plant viruses is believed to occur by one of two methods. One possibility (i.e. tobacco mosaic virus) is through the alteration of the plant's plasmodesmata. The second method (i.e. cowpea mosaic virus) uses cell wallspanning tubules. Using immunocytochemistry, localization of ORF1, ORF3, and the CP was performed. The ORF1 protein was found to localize near plasmodesmata, indicating that this viral protein is involved in cell-to-cell movement. There was no evidence of tubule formation. The ORF3 protein did not localize to any specific areas within a cell, although higher concentrations of this protein were found in the xylem vascular cells. The SBMV-C CP was also found to localize in plasmodesmata, indicating a possible role in cell-to-cell movement of SBMV-C. Based on the results of this study, it is proposed that SBMV-C traffics as viral particles, but does not move cell-to-cell via tubules. Instead, the vims moves through the plant's plasmodesmata through the activity of the ORF1 protein and possibly the CP. The long distance movement characteristics of SBMV-C were also studied. The accumulation of the ORF1 and CP in the secondary cell walls of the sieve elements suggests a role for these proteins in systemic movement of SBMV-C.

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