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

<div><p>The filamentous fungus <i>Aspergillus nidulans</i> primarily reproduces by forming asexual spores called conidia, the integrity of which is governed by the NF-κB type <i>velvet</i> 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 <u><b>V</b></u>osA/VelB-<u><b>a</b></u>ctivated <u><b>d</b></u>evelopmental genes, called <i>vadA</i>, 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 <i>vadA</i> indicate that VadA is required for proper downregulation of <i>brlA</i>, <i>fksA</i>, and <i>rodA</i>, and for proper expression of <i>tpsA</i> and <i>orlA</i> during sporogenesis. Moreover, <i>vadA</i> 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 <i>vadA</i> 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 <i>A</i>. <i>nidulans</i>.</p>