Identification of mimp-associated effector genes in Fusarium oxysporum f. sp. cubense race 1 and race 4 and virulence confirmation of a candidate effector gene.

Effectors secreted by microbes contribute to pathogen virulence and/or avirulence on host plants in the interaction of plants and microbes. Also, the effector repertoire determines the host specificity of a pathogen. Fusarium oxysporum f. sp. cubense (Foc) is the causal agent of banana wilt; however, knowledge about Foc effector genes is very limited. In this study, genome-wide effector gene identification was performed in Foc race 1 (Foc 1) and Foc race 4 (Foc 4) based on the context association between the effector genes and the transposable element mimp. A total of 20 candidate effector genes were identified, of which 3 were Foc 1-specific, 6 were Foc 4-specific, and 11 were present in both Foc 1 and Foc 4. Most genes (14 out of 20) showed a significant transcriptional burst in planta compared with in-culture conditions, from more than 10-fold to 1,617-fold, and at the highest 32,725-fold. In addition to Foc 1- and Foc 4-specific genes, the genes Foc 283, Foc 495, and Foc 594 also exhibited transcriptional race specificity. Sixteen of the twenty genes were predicted to have a signal peptide, nine genes might encode real effectors predicted by EffectorP 2.0, and eight genes had predicted motifs. To validate the pathogenicity of the candidate effector genes, we generated knockout mutant and complementants of the gene Foc 1324 and tested their virulence on banana plants. The results showed that Foc 1324 was a virulent factor and required for the pathogenicity of Foc 4.