UBL1 of F usarium verticillioides links the N ‐end rule pathway to extracellular sensing and plant pathogenesis

Abstract

Summary F usarium verticillioides produces fumonisin mycotoxins during colonization of maize. Currently, molecular mechanisms underlying responsiveness of F . verticillioides to extracellular cues during pathogenesis are poorly understood. In this study, insertional mutants were created and screened to identify genes involved in responses to extracellular starch. In one mutant, the restriction enzyme‐mediated integration cassette disrupted a gene ( UBL1 ) encoding a UBR ‐Box/ RING domain E 3 ubiquitin ligase involved in the N ‐end rule pathway. Disruption of UBL1 in F . verticillioides (Δ ubl1 ) influenced conidiation, hyphal morphology, pigmentation and amylolysis. Disruption of UBL1 also impaired kernel colonization, but the ratio of fumonisin B 1 per unit growth was not significantly reduced. The inability of a Δ ubl1 mutant to recognize an N ‐end rule degron confirmed involvement of UBL1 in the N ‐end rule pathway. Additionally, U bl1 physically interacted with two G protein α subunits of F . verticillioides , thus implicating UBL1 in G protein‐mediated sensing of the external environment. Furthermore, deletion of the UBL1 orthologue in F . graminearum reduced virulence on wheat and maize, thus indicating that UBL1 has a broader role in virulence among F usarium species. This study provides the first linkage between the N ‐end rule pathway and fungal pathogenesis, and illustrates a new mechanism through which fungi respond to the external environment.

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