Microcosm experiments show endless cycles of host and parasite adaptation in near natural populations.

Background: Translation initiation factors of the 4E and 4G protein families mediate resistance to several RNA plant viruses in the natural diversity of crops. Particularly, a single point mutation in melon eukaryotic translation initiation factor 4E (eIF4E) controls resistance toMelon necrotic spot virus(MNSV) in melon. Identification of allelic variants within natural populations by EcoTILLING has become a rapid genotype discovery method.Results: A collection ofCucumisspp. was characterised for susceptibility to MNSV andCucumber vein yellowing virus(CVYV) and used for the implementation of EcoTILLING to identify new allelic variants ofeIF4E. A high conservation ofeIF4Eexonic regions was found, with six polymorphic sites identified out of EcoTILLING 113 accessions. Sequencing of regions surrounding polymorphisms revealed that all of them corresponded to silent nucleotide changes and just one to a non-silent change correlating with MNSV resistance. Except for the MNSV case, no correlation was found between variation of eIF4E and virus resistance, suggesting the implication of different and/or additional genes in previously identified resistance phenotypes. We have also characterized a new allele ofeIF4EfromCucumis zeyheri, a wild relative of melon. Functional analyses suggested that this neweIF4Eallele might be responsible for resistance to MNSV.Conclusion: This study shows the applicability of EcoTILLING inCucumisspp., but given the conservation of eIF4E, new candidate genes should probably be considered to identify new sources of resistance to plant viruses. Part of the methodology described here could alternatively be used in TILLING experiments that serve to generate neweIF4Ealleles.