ABSTRACT
BACKGROUND: The eukaryotic translation initiation factor eIF4E plays a key role in plant-potyvirus interactions. eIF4E belongs to a small multigenic family and three genes, eIF4E1, eIF4E2 and eIF(iso)4E, have been identified in tomato. It has been demonstrated that eIF4E-mediated natural recessive resistances against potyviruses result from non-synonymous mutations in an eIF4E protein, which impair its direct interaction with the potyviral protein VPg. In tomato, the role of eIF4E proteins in potyvirus resistance is still unclear because natural or induced mutations in eIF4E1 confer only a narrow resistance spectrum against potyviruses. This contrasts with the broad spectrum resistance identified in the natural diversity of tomato. These results suggest that more than one eIF4E protein form is involved in the observed broad spectrum resistance. METHODOLOGY/PRINCIPAL FINDINGS: To gain insight into the respective contribution of each eIF4E protein in tomato-potyvirus interactions, two tomato lines silenced for both eIF4E1 and eIF4E2 (RNAi-4E) and two lines silenced for eIF(iso)4E (RNAi-iso4E) were obtained and characterized. RNAi-4E lines are slightly impaired in their growth and fertility, whereas no obvious growth defects were observed in RNAi-iso4E lines. The F1 hybrid between RNAi-4E and RNAi-iso4E lines presented a pronounced semi-dwarf phenotype. Interestingly, the RNAi-4E lines silenced for both eIF4E1 and eIF4E2 showed broad spectrum resistance to potyviruses while the RNAi-iso4E lines were fully susceptible to potyviruses. Yeast two-hybrid interaction assays between the three eIF4E proteins and a set of viral VPgs identified two types of VPgs: those that interacted only with eIF4E1 and those that interacted with either eIF4E1 or with eIF4E2. CONCLUSION/SIGNIFICANCE: These experiments provide evidence for the involvement of both eIF4E1 and eIF4E2 in broad spectrum resistance of tomato against potyviruses and suggest a role for eIF4E2 in tomato-potyvirus interactions.
Subject(s)
Disease Resistance/genetics , Eukaryotic Initiation Factor-4E/genetics , Gene Knockdown Techniques , Plant Diseases/virology , Potyvirus/physiology , Solanum lycopersicum/genetics , Solanum lycopersicum/virology , Blotting, Northern , Fertility/genetics , Gene Expression Regulation, Plant , Genes, Plant/genetics , Solanum lycopersicum/growth & development , Plant Diseases/genetics , Plants, Genetically Modified , Protein Binding , RNA Interference , RNA, Messenger/genetics , RNA, Messenger/metabolism , Ribonucleoproteins/metabolism , Transformation, Genetic , Transgenes/genetics , Two-Hybrid System Techniques , Viral Nonstructural Proteins/metabolismABSTRACT
The potential of a new in vitro inoculation and propagation method developed for Lettuce mosaic virus (LMV) on lettuce (Lactuca sativa L.) was evaluated by studying LMV infection on in vitro cultivated seedlings or on newly regenerated plantlets. Lettuce cultivars differing by their LMV-resistance status were inoculated with various natural LMV isolates as well as with Green Fluorescent Protein (GFP)-tagged recombinant virus isolates. A good correlation was observed between the known resistance status of the cultivars and the results obtained by in vitro screening. The results show that this resistance assay can be greatly improved by the use of GFP-tagged virus isolates. The main advantages of this method are reduced space requirements and an improved environmental safety, especially for the handling of recombinant virus, of quarantine virus or of transgenic plants.
