AUTHOR=Yang Wenjing , Wu Hao , Wang Zhangxun , Sun Qian , Qiao Lintao , Huang Bo 

TITLE=The APSES Gene MrStuA Regulates Sporulation in Metarhizium robertsii

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01208

DOI=10.3389/fmicb.2018.01208

ISSN=1664-302X

ABSTRACT=<p>The APSES family is a unique family of transcription factors with a basic helix-loop-helix structure (APSES: <italic>Asm1p, Phd1p, Sok2p, Efg1p</italic>, and <italic>StuAp</italic>), which are key regulators of cell development and sporulation-related processes. However, the functions of the APSES family of genes in the entomopathogenic fungus <italic>Metarhizium robertsii</italic> have not been reported. Here, we report the identification and characterization of the <italic>MrStuA</italic> gene, a member of the APSES family, in <italic>M. robertsii</italic>. The selected gene was identified as <italic>StuA</italic> in <italic>M. robertsii</italic> (<italic>MrStuA</italic>) because the gene product contains two conserved sequences, an APSES-type DNA-binding domain and a KilA DNA-binding domain, and has the highest homology with the StuA in the C-II clade of the APSES family. We found that the number of conidia produced by the Δ<italic>MrStuA</italic> strain was 94.45% lower than that in the wild type. Additionally, in the mutant, the conidia displayed an elongated shape, the sporulation was sparse and the phialide were slender. In addition, transcription levels of two central regulators of asexual development, <italic>AbaA</italic> and <italic>WetA</italic>, were significantly reduced in the mutant; furthermore, the transcription levels of other sporulation related genes, such as <italic>Mpk, Phi, Med, Aco, Flu</italic>, and <italic>FlbD</italic>, also decreased significantly. We also show that the median lethal time (LT<sub>50</sub>) of the mutant increased by 19%. This increase corresponded with a slower growth rate and an earlier conidia germination time compared to that of the wild strain. However, the resistance of the mutant to chemicals or physical stressors, such as ultraviolet radiation or heat, was not significantly altered. Our results indicate that in <italic>M. robertsii, MrStuA</italic> may play a crucial role in regulating sporulation as well as virulence, germination, and vegetative growth. This study improves our understanding of the impact of the transcription factor StuA on sporulation processes in filamentous fungi and provides a basis for further studies aimed at improving sporulation efficiency of these fungi for use as a biocontrol agent.</p>