Silencing of the Mitogen-Activated Protein Kinases (MAPK) Fus3 and Slt2 in Pseudocercospora fijiensis Reduces Growth and Virulence on Host Plants

Francis Onyilo, Geoffrey Tusiime, Jaindra N. Tripathi, Li-Hung Chen, Bryce Falk, Ioannis Stergiopoulos, Wilberforce Tushemereirwe, Jerome Kubiriba, Leena Tripathi

Pseudocercospora fijiensis , causal agent of the black Sigatoka disease (BSD) ofMusaspp., has spread globally since its discovery in Fiji 1963toall the banana and plantain growing areas across the globe. It is becoming the most damaging and economically important disease of this crop. The identification and characterization of genes that regulate infection processes and pathogenicity inP. fijiensiswill provide important knowledge for the development of disease-resistant cultivars. In many fungal plant pathogens, theFus3andSlt2are reported to be essential for pathogenicity.Fus3regulates filamentous-invasion pathways including the formation of infection structures, sporulation, virulence, and invasive and filamentous growth, whereasSlt2is involved in the cell-wall integrity pathway, virulence, invasive growth, and colonization in host tissues. Here, we used RNAi-mediated gene silencing to investigate the role of theSlt2andFus3homologs inP. fijiensisin pathogen invasiveness, growth and pathogenicity. ThePfSlt2andPfFus3silencedP. fijiensistransformants showed significantly lower gene expression and reduced virulence, invasive growth, and lower biomass in infected leaf tissues of East African Highland Banana (EAHB). This study suggests thatSlt2andFus3MAPK signaling pathways play important roles in plant infection and pathogenic growth of fungal pathogens. The silencing of these vital fungal genes through host-induced gene silencing (HIG) could be an alternative strategy for developing transgenic banana and plantain resistant to BSD.