FoCupin1, a Cupin_1 domain-containing protein, is necessary for the virulence of Fusarium oxysporum f. sp. cubense tropical race 4

Abstract

<i>Fusarium oxysporum</i> f. sp. <i>cubense</i> tropical race 4 (Foc TR4) is an important soilborne fungal pathogen that causes the most devastating banana disease. Effectors secreted by microbes contribute to pathogen virulence on host plants in plant-microbe interactions. However, functions of Foc TR4 effectors remain largely unexplored. In this study, we characterized a novel cupin_1 domain-containing protein (FoCupin1) from Foc TR4. Sequence analysis indicated that the homologous proteins of FoCupin1 in phytopathogenic fungi were evolutionarily conserved. Furthermore, FoCupin1 could suppress BAX-mediated cell death and significantly downregulate the expression of defense-related genes in tobacco by using the <i>Agrobacterium</i>-mediated transient expression system. <i>FoCupin1</i> was highly induced in the early stage of Foc TR4 infection. The deletion of <i>FoCupin1</i> gene did not affect Foc TR4 growth and conidiation. However, <i>FoCupin1</i> deletion significantly reduced Foc TR4 virulence on banana plants, which was further confirmed by biomass assay. The expression of the defense-related genes in banana was significantly induced after inoculation with <i>FoCupin1</i> mutants. These results collectively indicate <i>FoCupin1</i> is a putative effector protein that plays an essential role in Foc TR4 pathogenicity. These findings suggest a novel role for cupin_1 domain-containing proteins and deepen our understanding of effector-mediated Foc TR4 pathogenesis.