A Cell Wall Integrity–Related MAP Kinase Kinase Kinase <i>AflBck1</i> Is Required for Growth and Virulence in Fungus <i>Aspergillus flavus</i>

Abstract

<i>Aspergillus flavus</i> represents an important fungal pathogen, causing severe economic losses in crops. The mitogen-activated protein (MAP) kinase signaling pathway contributes to many physiological processes, but its precise role in <i>A. flavus</i> is not yet fully understood. In this study, we focused on the <i>AflBck1</i> gene, which encodes a MAP kinase kinase kinase of the Slt2-MAPK pathway. Targeted deletion of <i>AflBck1</i> led to a significant defect in growth and development, and a <i>AflBck1</i>-deleted mutant (∆<i>AflBck1</i>) showed higher sensitivity to cell-wall stress than wild type (WT). Importantly, we observed that ∆<i>AflBck1</i> displayed an enhanced ability to produce aflatoxin, a potential carcinogenic mycotoxin. However, the pathogenicity of the ∆<i>AflBck1</i> mutant was markedly reduced in peanut seeds. We also presented evidence that AflBck1 was genetically epistatic to AflMkk2 in the Slt2-MAPK pathway. Finally, we found that loss of the proline-rich region at the N terminus of AflBck1 affected the reproduction of <i>A. flavus</i>. Collectively, this study not only extended the understanding that the MAPK pathway regulated <i>A. flavus</i> pathogenicity but also provided a possible strategy to control <i>A. flavus</i> contamination.