Differential gene expression in nematode-susceptible and -tolerant East African highland bananas following inoculation with non-pathogenic Fusarium oxysporum endophytes

Endophytic non-pathogenic Fusarium oxysporum isolates have been shown to reduce Radopholus similis populations through induced resistance. We used cDNA-AFLPs to identify genes induced in banana plants susceptible (cv Nabusa, AAA-EA) and tolerant (cv Kayinja, ABB) to the nematode following colonization by endophytic isolates Emb2.4o and V5w2. Nematode challenge of plants was carried out 30 days after endophyte inoculation and roots harvested for RNA extraction 3 days later. Fifty up-regulated genes were assigned putative identities. Of interest to the current study was the up-regulation of genes involved in signal transduction, cell wall strengthening, the jasmonic acid pathway and transport of defence molecules. The expression profiles of differentially expressed fragments with similarity to ABC transporter, coronatine insensitive 1 (COI1), lipoxygenase (LOX) and â 1,3-glucan synthase genes were confirmed using quantitative real-time PCR. Challenge of endophyte-inoculated plants with R. similis resulted in further up-regulation of the activities of â-1,3-glucan synthase and COI1 in the susceptible cv Nabusa, and that of COI1 and LOX in the tolerant cv Kayinja. Our results confirm induced resistance as a mode of action for F. oxysporum endophyte control of R. similis in banana. This investigation represents the first report of the isolation and identification of genes involved in the interaction between endophytic F. oxysporum and banana.