The secondary metabolite regulator, BbSmr1, is a central regulator of conidiation via the BrlA‐AbaA‐WetA pathway in Beauveria bassiana

Abstract

Summary The filamentous fungus Beauveria bassiana, an insect fungal pathogen, is widely used for pest biocontrol. Aerial conidia are infectious propagules, and their yield and viability greatly affect the field application of this fungus; however, little is known about the molecular regulatory mechanism of the triggered conidiation. In the present study, we find that the secondary metabolite regulator BbSmr1 is involved in the regulation of asexual conidiation development and stress response in B. bassiana. A deficiency in Bbsmr1 results in a prominent fluffy‐like phenotype on solid medium, decreased conidial yield, accelerated conidial germination, as well as increased tolerance to H2O2 stress and cell wall inhibitors. The deletion of Bbsmr1 also leads to thickened conidial cell walls and changed cell epitopes. Overexpressing either BbbrlA or BbabaA in the ∆Bbsmr1 strain can rescue the phenotypes of conidial development and stress response. BbSmr1 activates BbbrlA transcription by directly binding to the A4GA3 sequence of the BbbrlA promoter. BbBrlA in turn binds to the promoter of Bbsmr1 and negatively regulates the expression of Bbsmr1. These results indicate that BbSmr1 positively regulates conidial development in B. bassiana by activating the central development pathway BrlA‐AbaA‐WetA and provides insights into the developmental regulatory mechanism of entomopathogenic fungi.

Regulatory Effects of Nitric Oxide on Reproduction and Melanin Biosynthesis in Onion Pathogenic Fungus Stemphylium Eturmiunum

“…7A), which suggests that NO-producing capacity can be self-regulated in response to alteration of the cellular NO levels. In addition, SNP supplement at concentrations lower than 0.2 mmol/L also promotes conidiation, which implicates that external application of NO at lower concentrations favors the transcription of brlA, abaA, and wetA, the three transcriptional factors involved in conidiation (Chen et al 2020).…”

The Zinc Finger Transcription Factor BbCmr1 Regulates Conidium Maturation in Beauveria bassiana

“…Deletion of Bbsmr1 resulted in fewer conidia but increased conidial resistance against adverse conditions. Transcriptome analysis further identified several transcription factors with significantly changed expression levels in the Bbsmr1 deletion mutant compared to the wild type ( 27 ). Among them, a putative GAL4-like Zn 2 Cys 6 transcription factor ( EJP63695.1 ) was upregulated in the Bbsmr1- deleted mutant and named BbCmr1.…”

“…BrlA is required for conidiophore development and binds the CCCCT motif ( 27 ). This motif was found in the Bbcmr1 promoter, implying that BbBrlA could directly regulate Bbcmr1 expression.…”

“…However, it remains unknown whether there are other regulatory proteins involved in conidium maturation. Our previous study implied the functional role of BbSmr1 in conidiation and the production of secondary metabolites ( 8 , 27 ). We compared the results of conidial RNA sequencing (RNA-seq) of ΔBbsmr1 with WT and identified a transcription factor, BbCmr1 ( c onidium m aturation r egulator 1 ), involved in regulating conidial development.…”

“…The conidiation event was temporally and spatially controlled by the developmental regulatory cascade BrlA-AbaA-WetA ( 20 , 27 , 34 ). The initiation and maturation of conidia are two distinct processes during conidial development in filamentous fungi and are regulated by different transcription factors ( 35 ).…”