The role of VosA/VelB-activated developmental gene vadA in Aspergillus nidulans

The filamentous fungus Aspergillus nidulans primarily reproduces by forming asexual spores called conidia, the integrity of which is governed by the NF-κB type velvet regulators VosA and VelB. The VosA-VelB hetero-complex regulates the expression of spore-specific structural and regulatory genes during conidiogenesis. Here, we characterize one of the V osA/VelB- a ctivated d evelopmental genes, called vadA , the expression of which in conidia requires activity of both VosA and VelB. VadA (AN5709) is predicted to be a 532-amino acid length fungal-specific protein with a highly conserved domain of unknown function (DUF) at the N-terminus. This DUF was found to be conserved in many Ascomycota and some Glomeromycota species, suggesting a potential evolutionarily conserved function of this domain in fungi. Deletion studies of vadA indicate that VadA is required for proper downregulation of brlA , fksA , and rodA , and for proper expression of tpsA and orlA during sporogenesis. Moreover, vadA null mutant conidia exhibit decreased trehalose content, but increased β(1,3)-glucan levels, lower viability, and reduced tolerance to oxidative stress. We further demonstrate that the vadA null mutant shows increased production of the mycotoxin sterigmatocystin. In summary, VadA is a dual-function novel regulator that controls development and secondary metabolism, and participates in bridging differentiation and viability of newly formed conidia in A . nidulans .