Exploring natural variations in eIF4E and screening for potyviral resistance in diverse Nicotiana species

The eukaryotic translation factors, including eIF4E which plays a major role in host translation initiation by recruiting messenger RNAs to the ribosomal complex, have repeatedly been identified as host factors required for viral infection. The cDNA sequence of eIF4E and eIF(iso)4E from 16 different genotypes, including 8 Nicotiana species and 8 Nicotiana tabacum cultivars, were determined in this study. The consensus Nicotiana eIF4E cDNA is 669 nucleotides long and codes for 222 amino acids. A high level of similarity was detected among eIF4E proteins of Nicotiana species sharing over 97% nucleotide identity and 95% amino acid identity in most cases. The eIF4E from tobacco (Nicotiana tabacum) shares a protein identities of 75.7% with pepper-eIF4E, 74.3% with tomato-eIF4E, 73.4% with potato-eIF4E, 73.1% with melon-eIF4E, 72.6% with cucumber-eIF4E, 73.1% with lettuce-eIF4E, and 71.5% with pea-eIF4E. In the case of eIF(iso)4E, the cDNA is 603 nucleotides long and codes for 200 amino acids. In this study, we investigated variations which exist in eIF4E or eIF(iso)4E, and attempted to correlate the variations which exist in these translation initiation factors with the resistance phenotype against several potyviruses in Nicotiana plants. We detected amino acid substitutions at the 18 positions for eIF4E and substitutions at the 11 positions for eIF(iso)4E. We attempted to correlate the resistance against Potato virus Y (PVY) or Pepper mottle virus (PepMoV) with the natural variations detected within the Nicotiana genotypes. However, no variation responsible for the gains of potyviral resistance was detected in this study. The result suggests that the potyviral resistance observed in Nicotiana species against PVY and PepMoV was conferred by an unknown resistance factor other than eIF4E or eIF(iso)4E, unlike general potyviral resistance observed in other plant species of the Solanaceae family.