AUTHOR=Kocsis Beatrix , Lee Mi-Kyung , Yu Jae-Hyuk , Nagy Tibor , Daróczi Lajos , Batta Gyula , Pócsi István , Leiter Éva 

TITLE=Functional analysis of the bZIP-type transcription factors AtfA and AtfB in Aspergillus nidulans

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1003709

DOI=10.3389/fmicb.2022.1003709

ISSN=1664-302X

ABSTRACT=<p>Transcription factors (TFs) with the basic leucin zipper domain are key elements of the stress response pathways in filamentous fungi. In this study, we functionally characterized the two bZIP type TFs AtfA and AtfB by deletion (<italic>Δ</italic>) and overexpression (OE) of their encoding genes in all combination: <italic>ΔatfA, ΔatfB, ΔatfAΔatfB, ΔatfAatfB</italic>OE, <italic>ΔatfBatfA</italic>OE, <italic>atfA</italic>OE, <italic>atfB</italic>OE and <italic>atfA</italic>OE<italic>atfB</italic>OE in <italic>Aspergillus nidulans</italic>. Based on our previous studies, <italic>ΔatfA</italic> increased the sensitivity of the fungus to oxidative stress mediated by menadione sodium bisulfite (MSB) and tert-butylhydroperoxide (<italic>t</italic>BOOH), while <italic>ΔatfB</italic> was not sensitive to any oxidative stress generating agents, namely MSB, <italic>t</italic>BOOH and diamide at all. Contrarily, the <italic>ΔatfB</italic> mutant was sensitive to NaCl, but tolerant to sorbitol. Overexpression of <italic>atfB</italic> was able to compensate the MSB sensitivity of the <italic>ΔatfA</italic> mutant. Heavy metal stress elicited by CdCl<sub>2</sub> reduced diameter of the <italic>atfB</italic>OE and <italic>atfA</italic>OE<italic>atfB</italic>OE mutant colonies to about 50% of control colony, while the cell wall stress generating agent CongoRed increased the tolerance of the <italic>ΔatfA</italic> mutant. When we tested the heat stress sensitivity of the asexual spores (conidiospores) of the mutants, we found that conidiospores of <italic>ΔatfAatfB</italic>OE and <italic>ΔatfBatfA</italic>OE showed nearly 100% tolerance to heat stress. Asexual development was negatively affected by <italic>ΔatfA</italic>, while <italic>atfA</italic>OE and <italic>atfA</italic>OE coupled with <italic>ΔatfB</italic> increased the number of conidiospores of the fungus approximately 150% compared to the control. Overexpression of <italic>atfB</italic> led to a 25% reduction in the number of conidiospores, but increased levels of <italic>abaA</italic> mRNA and size of conidiospores. Sexual fruiting body (cleistothecium) formation was diminished in the <italic>ΔatfA</italic> and the <italic>ΔatfAΔatfB</italic> mutants, while relatively elevated in the <italic>ΔatfB</italic> and the <italic>ΔatfBatfA</italic>OE mutants. Production of the mycotoxin sterigmatocystin (ST) was decreased to undetectable levels in the <italic>ΔatfA</italic> mutant, yet ST production was restored in the <italic>ΔatfAΔatfB</italic> mutant, suggesting that <italic>ΔatfB</italic> can suppress ST production defect caused by <italic>ΔatfA</italic>. Levels of ST were also significantly decreased in the <italic>ΔatfAatfB</italic>OE, <italic>ΔatfBatfA</italic>OE and <italic>atfA</italic>OE<italic>atfB</italic>OE mutants.</p>