Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2002
Publication Date: 10/2/2002
Citation: LEE, L., PALUKAITIS, P., GRAY, S.M. HOST-DEPENDENT REQUIREMENT FOR THE POTATO LEAFROLL VIRUS 17-KDA PROTEIN IN VIRUS MOVEMENT. MOLECULAR PLANT MICROBE INTERACTIONS. 2002. Interpretive Summary: Potato leafroll virus (PLRV) causes severe yield losses in potato and has a world-wide distribution. This virus is transmitted by aphids and viral infection is restricted to the plant vascular tissue. One protein, P17, encoded by the PLRV genome has biochemical properties similar to "movement proteins" of other viruses. These proteins regulate the movement of viruses between cells and within vascular tissues. The biological activit of the PLRV P17 has not been studied. In this paper, we investigated the requirement for the P17 in PLRV infection of four plant species. The P17 was essential for PLRV infection of potato and a common weed host, but the P17 was not required for the virus to infect two tobacco species commonly used in laboratory studies. However, the lack of the P17 did slow down the ability of the virus to move within the tobacco species and the virus was not able to infect older tissues on the plants. Interestingly, the reaction observed in tobacco resembles the reaction found in some potato cultivars that have partial resistance to PLRV and suggests the resistance mechanisms may adversely, but incompletely, affect the P17 function. Understanding the role of the P17 in virus movement in plants may aid in understanding and developing new types of resistance in plants that more completely restrict the spread of PLRV away from the initial site of infection.
Technical Abstract: The requirement for the 17-kDa protein (17K) of Potato leafroll virus (PLRV) in virus movement was investigated in four plant species; potato (Solanum tuberosum), cultivars Desiree and Russet Burbank; Physalis floridana, a common woody host; and two species commonly used in laboratory studies, Nicotiana benthamiana and N. clevelandii. Two mutant viruses were echaracterized, one that does not translate the 17K protein, and another that should express a 17K protein missing the first four amino acids. The mutant PLRV viruses were able to replicate and accumulate in agroinoculated leaves of potato and P. floridana, but they were unable to move into vascular tissues and initiate systemic infection of these plants. In contrast, the mutant viruses were able to spread systemically from inoculated leaves in both Nicotiana species, although, the efficiency of infection was reduced relative to wild-type virus. Examination of virus distribution in N. benthamiana plants using tissue immunoblotting techniques revealed that the wild-type and mutant viruses followed a similar movement pathway out of the inoculated leaves. Virus first moved upward to the apical tissues, then downward. The mutant viruses infected fewer phloem-associated cells, were slower than wild-type virus to move out of the inoculated tissue and into apical tissues, and were unable to infect any mature leaves present on the plant at the time of inoculation.