Gα-cAMP/PKA pathway positively regulates pigmentation, chaetoglobosin A biosynthesis and sexual development in Chaetomium globosum.

Yang Hu,Oren Akhberdi,Xudong Zhu,Xiaoran Hao,Longfei Chen,Yanjie Liu,Xi Yu

doi:10.1371/journal.pone.0195553

Yang Hu, Oren Akhberdi + Show 5 more

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https://doi.org/10.1371/journal.pone.0195553

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Abstract

Sensing the environmental signals, the canonical Gα-cAMP/PKA pathway modulates mycelial growth and development, and negatively regulates some secondary metabolism in filamentous fungi, e.g. aflatoxin in Aspergillus nidulans. Here we report the characterization of this signaling pathway in Chaetomium globosum, a widely spread fungus known for synthesizing abundant secondary metabolites, e.g. chaetoglobosin A (ChA). RNAi-mediated knockdown of a putative Gα-encoding gene gna-1, led to plural changes in phenotype, e.g. albino mycelium, significant restriction on perithecium development and decreased production of ChA. RNA-seq profiling and qRT-PCR verified significantly fall in expression of corresponding genes, e.g. pks-1 and CgcheA. These defects could be restored by simultaneous knock-down of the pkaR gene encoding a regulatory subunit of cAMP-dependent protein kinase A (PKA), suggesting that pkaR had a negative effect on the above mentioned traits. Confirmatively, the intracellular level of cAMP in wild-type strain was about 3.4-fold to that in gna-1 silenced mutant pG14, and addition of a cAMP analog, 8-Br-cAMP, restored the same defects, e.g., the expression of CgcheA. Furthermore, the intracellular cAMP in gna-1 and pkaR double silenced mutant was approaching the normal level. The following activity inhibition experiment proved that the expression of CgcheA was indeed regulated by PKA. Down-regulation of LaeA/VeA/SptJ expression in gna-1 mutant was also observed, implying that Gα signaling may crosstalk to other regulatory pathways. Taken together, this study proposes that the heterotrimeric Gα protein-cAMP/PKA signaling pathway positively mediates the sexual development, melanin biosynthesis, and secondary metabolism in C. globosum.

Highlights

Chaetomium fungi are commonly found in the environment with more than 350 species described in this genus [1]
To gain insight into the regulation mechanism of ChA biosynthesis in C. globosum, we knocked down the gene gna-1 (CHGG_03321), Gα signaling positively regulates chaetoglobosin A biosynthesis putatively encoding a group I Gα protein, and the gene pkaR (CHGG_00688), encoding the regulatory subunit of the cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA). Using this established RNA interference (RNAi) strategy [15, 24], we demonstrated that the canonical G protein-cAMP/PKA pathway plays a pivotal role in the production of ChA in C. globosum NK102
To investigate whether the secondary metabolite ChA of C. globosum was under the control of the G protein-cAMP/PKA signaling pathway, genes gna-1 and pkaR, two key components in this pathway, were knocked down by RNAi

Summary

Introduction

Chaetomium fungi are commonly found in the environment with more than 350 species described in this genus [1]. Chaetoglobosins are grouped into the cytochalasin family of natural products and are polyketide derivatives found in fungi [7]. They have unique biochemical property of binding eukaryotic actin proteins, disturbing the normal actin network in the cell. They display strong cytotoxicity against tumor cell lines [8, 9], phytotoxicity on numerous plants [10], immunomodulatory activities [11], and antifungal [12] and nematicidal activities [13]. We previously observed in C. globosum NK102 that a polyketide synthase gene, pks-1, was required for both colonial pigmentation and biosynthesis of chaetoglobosin A (ChA) via an unknown mechanism [15]

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