The capacity of Aspergillus niger to sense and respond to cell wall stress requires at least three transcription factors: RlmA, MsnA and CrzA

Abstract

BackgroundCell wall integrity, vesicle transport and protein secretion are key factors contributing to the vitality and productivity of filamentous fungal cell factories such as Aspergillus niger. In order to pioneer rational strain improvement programs, fundamental knowledge on the genetic basis of these processes is required. The aim of the present study was thus to unravel survival strategies of A. niger when challenged with compounds interfering directly or indirectly with its cell wall integrity: calcofluor white, caspofungin, aureobasidin A, FK506 and fenpropimorph.ResultsTranscriptomics signatures of A. niger and phenotypic analyses of selected null mutant strains were used to predict regulator proteins mediating the survival responses against these stressors. This integrated approach allowed us to reconstruct a model for the cell wall salvage gene network of A. niger that ensures survival of the fungus upon cell surface stress. The model predicts that (i) caspofungin and aureobasidin A induce the cell wall integrity pathway as a main compensatory response via induction of RhoB and RhoD, respectively, eventually activating the mitogen-activated protein kinase kinase MkkA and the transcription factor RlmA. (ii) RlmA is the main transcription factor required for the protection against calcofluor white but it cooperates with MsnA and CrzA to ensure survival of A. niger when challenged with caspofungin and aureobasidin A. (iii) Membrane stress provoked by aureobasidin A via disturbance of sphingolipid synthesis induces cell wall stress, whereas fenpropimorph-induced disturbance of ergosterol synthesis does not.ConclusionThe present work uncovered a sophisticated defence system of A. niger which employs at least three transcription factors - RlmA, MsnA and CrzA – to protect itself against cell wall stress. The transcriptomic data furthermore predicts a fourth transfactor, SrbA, which seems to be specifically important to survive fenpropimorph-induced cell membrane stress. Future studies will disclose how these regulators are interlocked in different signaling pathways to secure survival of A. niger under different cell wall stress conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s40694-014-0005-8) contains supplementary material, which is available to authorized users.

A Transcriptome Meta-Analysis Proposes Novel Biological Roles for the Antifungal Protein AnAFP in Aspergillus niger

“…In most of the studies, A . niger (N402 or derivatives thereof) was cultivated under controlled submerged conditions in bioreactors and stressed either during germination [37, 43, 44] or during the exponential growth phase [45]. Interestingly, none of the secretion stress agents (DTT, tunicamycin) and none of the cell membrane or cell-wall stressors applied in these studies (caspofungin, fenpropimorph, FK506, aureobasidin A, natamycin) provoked an increase in anafp expression.…”

“…Finally, deletion of two transcription factors important for securing cell wall integrity of A . niger (RlmA, [44]; TupA, [47] did also not affect anafp expression. Likewise, confrontation of A .…”

Transcriptomic and molecular genetic analysis of the cell wall salvage response ofAspergillus nigerto the absence of galactofuranose synthesis

“…In A. niger the requirement of RlmA for the induction of the α‐glucan synthase A gene ( agsA ) in response to Calcofluor white has been established (Damveld et al, 2005). Deletion of RlmA renders A. niger sensitive to Calcofluor white, and to a lesser extent also to other cell wall disturbing agents such as caspofungin (CA), aureobasidinA (AbaA), FK506 or fenpropimorph (FP), indicating that other remodelling mechanisms might exist (Fiedler et al, ). In the same study, transcription factor binding site enrichment analysis of differentially expressed genes in response to CA, AbaA, FK506 and FP was performed, which identified possible involvement of both RlmA and MsnA (homolog of Msn2/4 in S. cerevisiae ) transcription factors in counteracting CA‐induced cell wall stress.…”

“…In the same study, transcription factor binding site enrichment analysis of differentially expressed genes in response to CA, AbaA, FK506 and FP was performed, which identified possible involvement of both RlmA and MsnA (homolog of Msn2/4 in S. cerevisiae ) transcription factors in counteracting CA‐induced cell wall stress. Indeed, deletion of the MsnA transcription factor, like deletion of the RlmA transcription factor, led to increased susceptibility towards CA (Fiedler et al, ). MsnA has been shown to be required for coping with several stress responses, including osmotic and oxidative stress (Han and Prade, ; Bose et al, ; Hong et al, ).…”

Comparative RNA-seq based transcriptomic analysis of Aspergillus nidulans recombinant strains overproducing heterologous glycoside hydrolases

“…Fiedler et al (2014) showed that A. niger senses and responds to cell wall stress with at least three transcription factors, RlmA, MsnA and CrzA 49 . Our transcriptomic data showed down-regulation of rlmA both in A. nidulans1542 and A. nidulansAbfA, indicating that these recombinant strains were regulated by cell wall stress caused by heterologous protein production 49 .…”