title: Inducible resistance to maize streak virus.
abstract: Maize streak virus (MSV), which causes maize streak disease (MSD), is the major viral pathogenic constraint on maize production in Africa. Type member of the Mastrevirus genus in the family Geminiviridae, MSV has a 2.7 kb, single-stranded circular DNA genome encoding a coat protein, movement protein, and the two replication-associated proteins Rep and RepA. While we have previously developed MSV-resistant transgenic maize lines constitutively expressing "dominant negative mutant" versions of the MSV Rep, the only transgenes we could use were those that caused no developmental defects during the regeneration of plants in tissue culture. A better transgene expression system would be an inducible one, where resistance-conferring transgenes are expressed only in MSV-infected cells. However, most known inducible transgene expression systems are hampered by background or "leaky" expression in the absence of the inducer. Here we describe an adaptation of the recently developed INPACT system to express MSV-derived resistance genes in cell culture. Split gene cassette constructs (SGCs) were developed containing three different transgenes in combination with three different promoter sequences. In each SGC, the transgene was split such that it would be translatable only in the presence of an infecting MSV's replication associated protein. We used a quantitative real-time PCR assay to show that one of these SGCs (pSPLITrepIII-Rb-Ubi) inducibly inhibits MSV replication as efficiently as does a constitutively expressed transgene that has previously proven effective in protecting transgenic maize from MSV. In addition, in our cell-culture based assay pSPLITrepIII-Rb-Ubi inhibited replication of diverse MSV strains, and even, albeit to a lesser extent, of a different mastrevirus species. The application of this new technology to MSV resistance in maize could allow a better, more acceptable product.
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Dionne N
authors.initials: DN
authors.lastname: Shepherd
authors.affiliation: Centre for Tropical Crops and Biocommodities, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dugdale
authors.affiliation: Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory, Cape Town, South Africa; Centre for High-Performance Computing, Rosebank, Cape Town, South Africa.
authors.forename: Darren P
authors.initials: DP
authors.lastname: Martin
authors.affiliation: School of Biological Sciences and Biomolecular Interaction Centre, University of Canterbury, Christchurch, New Zealand; Department of Plant Pathology and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America; Electron Microscope Unit, Division of Medical Biochemistry, Department of Clinical Laboratory Sciences, University of Cape Town, Observatory, Cape Town, South Africa.
authors.forename: Arvind
authors.initials: A
authors.lastname: Varsani
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Lakay
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Marion E
authors.initials: ME
authors.lastname: Bezuidenhout
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch, Cape Town, South Africa; Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory, Cape Town, South Africa.
authors.forename: Adérito L
authors.initials: AL
authors.lastname: Monjane
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Thomson
authors.affiliation: Centre for Tropical Crops and Biocommodities, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.
authors.forename: James
authors.initials: J
authors.lastname: Dale
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch, Cape Town, South Africa; Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory, Cape Town, South Africa.
authors.forename: Edward P
authors.initials: EP
authors.lastname: Rybicki
mesh_terms: D018929:Cell Culture Techniques; D060467:Disease Resistance; D016679:Genome, Viral; D026762:Maize streak virus / Q000235:genetics* / Q000276:immunology; D030821:Plants, Genetically Modified / Q000276:immunology / Q000821:virology*; D011401:Promoter Regions, Genetic; D019076:Transgenes; D014764:Viral Proteins / Q000235:genetics / Q000276:immunology; D014779:Virus Replication; D003313:Zea mays / Q000235:genetics* / Q000276:immunology* / Q000821:virology
chemical_list: D014764:Viral Proteins