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

Potassium (K⁺) is one of the most important macronutrients for plant growth and development. It is generally accepted that the KUP/HAK/KT transporters play essential roles in K⁺ uptake at low concentrations. However, their physiological functions in bananas remain unknown. Here, we cloned MaHAK5 and analyzed its functions in banana (Musa acuminata). Gene expression analysis showed that MaHAK5 was upregulated in the roots and leaves in the early stage of low K⁺ (LK) stress. MaHAK5 was localized in the cytomembrane. The expression of MaHAK5 improved the growth of the low K⁺-sensitive yeast mutant R5421 at different K⁺ supply levels. Overexpression of MaHAK5 in Arabidopsis thaliana significantly enhanced the ability for K⁺ uptake and increased the chlorophyll content under LK stress. These results indicate that MaHAK5 plays a crucial role in maintaining K⁺ uptake in bananas.