Author
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Brown, Charles |
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SMITH, O - HOOD COLLEGE, MD |
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Submitted to: Academic Press
Publication Type: Book / Chapter Publication Acceptance Date: 2/15/2001 Publication Date: 9/22/2001 Citation: BROWN, C.R., SMITH, O.P. APPROACHES TO THE GENETIC ENGINEERING OF POTATO FOR RESISTANCE TO POTATO LEAFROLL VIRUS. ACADEMIC PRESS, VIRUS-INSECT-PLANT INTERACTIONS, EDS. HARRIS, R., DRILLUS,T., SMITH, 0. CH 12:233-246. 2001. Interpretive Summary: Potato leafroll virus (PLRV) is one of the most damaging viruses of potato. It is transmitted by aphids and is controlled by production of virus free seedstock, insecticides, and occasionally by resistant cultivars. However there are no resistant cultivars suitable for the processing industry. In the Northwest 100 million dollars are spent annually to control this and other aphid transmitted viruses. Genetic engineering resistance to potato leafroll virus involves using a concept called pathogen derived resistance. This employs the insertion of gene from the virus into the plant genome and its expression in the wrong way or the wrong time so that the disease process that the virus causes is interfered with. Experience has shown that expression of the coat protein gene can lead to partial resistance to potato leafroll virus. Expression of any gene in an anti-sense fashion, i.e., the reverse structure of the gene so that there is no chance of expression, also can lead to expression of partial resistance. A significant breakthrough occurred when portions of or the entire length of the replicase gene were transformed into potato. Very high levels of resistance, approaching immunity, were recovered. Using the full length replicase was the best approach in terms of percent recovery of high levels of resistance and the resistance level. Despite success in identifying a good strategy, the mechanism of resistance for any of the transgenic approaches is not known. Use of transgenic replicase for PLRV resistance could potentially save considerable expense in virus control throughout the world. Gene insertion can convert a highly popular variety into PLRV resistor while maintaining the genotype intact, a result that is not possible with traditional sexual breeding. Technical Abstract: Potato leafroll virus (PLRV) is one of the most damaging viruses of potato. It is a member of the polerovirus group, being transmitted by aphids in a persistent manner. It is controlled by production of virus-free seed stock, insecticides, and occasionally by resistant cultivars. Insecticides are relatively effective because the acquisition and transmission times allow aphicides to block virus introduction spread to a certain degree. Transgenic are based on "pathogen-derived resistance" that employs the insertion of gene from the virus into the plant genome and its expression in the wrong way or at the wrong time so that the disease process that the virus causes is interfered with. Experience has shown that expression of the coat protein gene can lead to partial resistance to potato leafroll virus. Expression of any gene in an anti-sense fashion, i.e., the reverse structure of the gene so that there is no chance of expression, also can lead to partial resistance. The replicase is composed of two overlappin open-reading frames (ORF). Approximately 90% of the translation is limited to the first ORF while 10% employs a frame-shifting to translate through to the end of the second ORF. High levels of resistance, approaching immunity, were recovered when the full-length and partial replicase cistrons were expressed in potato. After inoculation, virus could not be detected either in the inoculated plants or in plants grown from the tubers of these plants. Despite success in identifying replicase as a good strategy, the mechanism of resistance for all of the transgenic approaches is not known. Gene insertion can convert a highly popular variety into PLRV resistor while maintaining the genotype intact, a result that is not possible with traditional sexual breeding of potato. |
