A complex eIF4E locus impacts the durability of va resistance to Potato virus Y in tobacco

Abstract

Many recessive resistances against potyviruses are mediated by eukaryotic translation initiation factor 4E (eIF4E). In tobacco, the va resistance gene commonly used to control Potato virus Y (PVY) corresponds to a large deletion affecting the eIF4E-1 gene on chromosome 21. Here, we compared the resistance durability conferred by various types of mutations affecting eIF4E-1 (deletions of various sizes, frameshift or nonsense mutations). The ‘large deletion’ genotypes displayed the broadest and most durable resistance, whereas frameshift and nonsense mutants displayed a less durable resistance, with rapid and frequent apparition of resistance-breaking variants. In addition, genetic and transcriptomic analyses revealed that resistance durability is strongly impacted by a complex genetic locus on chromosome 14, which contains three other eIF4E genes. One of these, eIF4E-3, is rearranged as a hybrid gene between eIF4E-2 and eIF4E-3 (eIF4E-2-3) in the genotypes showing the most durable resistance, while eIF4E-2 is differentially expressed between the tested varieties. RNA-seq and quantitative reverse transcriptase-polymerase chain reaction experiments demonstrated that eIF4E-2 expression level is positively correlated with resistance durability. These results suggest that besides the nature of the mutation affecting eIF4E-1, three factors linked with a complex locus may potentially impact va durability: loss of an integral eIF4E-3, presence of eIF4E-2-3 and overexpression of eIF4E-2. This latter gene might act as a decoy in a non-productive virus–plant interaction, limiting the ability of PVY to evolve towards resistance breaking. Taken together, these results show that va resistance durability can in large part be explained by complex redundancy effects in the eIF4E gene family.