The M35 Metalloprotease Effector FocM35_1 Is Required for Full Virulence of Fusarium oxysporum f. sp. cubense Tropical Race 4

Abstract

<i>Fusarium oxysporum</i> f. sp. <i>cubense</i> tropical race 4 (<i>Foc</i> TR4) causes Fusarium wilt of banana, the most devastating disease on a banana plant. The genome of <i>Foc</i> TR4 encodes many candidate effector proteins. However, little is known about the functions of these effector proteins on their contributions to disease development and <i>Foc</i> TR4 virulence. Here, we discovered a secreted metalloprotease, FocM35_1, which is an essential virulence effector of <i>Foc</i> TR4. FocM35_1 was highly upregulated during the early stages of <i>Foc</i> TR4 infection progress in bananas. The FocM35_1 knockout mutant compromised the virulence of <i>Foc</i> TR4. FocM35_1 could interact with the banana chitinase MaChiA, and it decreased banana chitinase activity. FocM35_1 induced cell death in <i>Nicotiana benthamiana</i> while suppressing the INF1-induced hypersensitive response (HR), and its predicted enzymatic site was required for lesion formation and the suppression to INF1-induced HR on <i>N. benthamiana</i> leaves. Importantly, treatment of banana leaves with recombinant FocM35_1 accelerates <i>Foc</i> TR4 infection. Collectively, our study provides evidence that metalloprotease effector FocM35 seems to contribute to pathogen virulence by inhibiting the host immunity.