Ontogenic Resistance in Apple

Ontogenic scab resistance in apple leaves and fruits is a horizontal resistance against the plant pathogen Venturia inaequalis and is expressed as decrease of disease symptoms and incidence with the ageing of the leaves. Several studies at biochemical level tried to unveil the nature of this resistance, however without any conclusive results. We decided therefore to investigate the genetic origin of this phenomenon by performing a full quantitative trascriptome sequencing and comparison of young (susceptible) and old (ontogenic resistant) leaves, infected or not with the pathogen. Two time points at 72 and 96 hours post inoculation were chosen for RNA sampling and sequencing. Comparison between the different conditions (young and old leaves, inoculated or not) should allow finding genes differentially expressed which may represent different induced plant defense reaction leading to ontogenic resistance or be the cause for a constitutive (not inoculated with the pathogen) shift toward resistance in old leaves. Differentially expressed genes were then characterized for their function by homology to A. thaliana and other plants' genes, particularly looking for genes involved in pathways already suspected of appertaining to ontogenic resistance in apple or other hosts, or to plant defense mechanisms in general.