Reconstruction of Signaling Networks Regulating Fungal Morphogenesis by Transcriptomics

Abstract

Coordinated control of hyphal elongation and branching is essential for sustaining mycelial growth of filamentous fungi. In order to study the molecular machinery ensuring polarity control in the industrial fungus Aspergillus niger, we took advantage of the temperature-sensitive (ts) apical-branching ramosa-1 mutant. We show here that this strain serves as an excellent model system to study critical steps of polar growth control during mycelial development and report for the first time a transcriptomic fingerprint of apical branching for a filamentous fungus. This fingerprint indicates that several signal transduction pathways, including TORC2, phospholipid, calcium, and cell wall integrity signaling, concertedly act to control apical branching. We furthermore identified the genetic locus affected in the ramosa-1 mutant by complementation of the ts phenotype. Sequence analyses demonstrated that a single amino acid exchange in the RmsA protein is responsible for induced apical branching of the ramosa-1 mutant. Deletion experiments showed that the corresponding rmsA gene is essential for the growth of A. niger, and complementation analyses with Saccharomyces cerevisiae evidenced that RmsA serves as a functional equivalent of the TORC2 component Avo1p. TORC2 signaling is required for actin polarization and cell wall integrity in S. cerevisiae. Congruently, our microscopic investigations showed that polarized actin organization and chitin deposition are disturbed in the ramosa-1 mutant. The integration of the transcriptomic, genetic, and phenotypic data obtained in this study allowed us to reconstruct a model for cellular events involved in apical branching.

Recent Advances on Filamentous Fungal Biofilms for Industrial Uses

“…Transcriptomics work on A. niger SSF is limited and the situation for Aspergillus biofilms is minimal but interesting work was published on SCF for several features [92][93][94][95][96]. Some results obtained with A. fumigatus biofilms have been already discussed elsewhere [1].…”

Dual transcriptional profiling of a bacterial/fungal confrontation: Collimonas fungivorans versus Aspergillus niger

“…Its product functions as a chitinase involved in cell wall remodeling and/or maturation (Yamazaki et al, 2008). During branching of A. niger hyphae, gene An09g06400 was downregulated (Meyer et al, 2009). Differential regulation of these genes suggests that the presence of Collimonas promotes changes in fungal cell wall dynamics, some of which are likely to be linked to the changes in hyphal morphology (Figure 2b).…”

Hyphal and cytoskeleton polarization in Tuber melanosporum: A genomic and cellular analysis

“…It has recently been shown that it is also present and functional in the filamentous fungus A. niger Meyer et al, 2010). In A. niger, it has been shown that a single point mutation in the RmsA gene is responsible for defective hyphal growth, suggesting its involvement in the elongation rate of the parent hypha prior to the appearance of apical branches ( Reynaga-Peña andBartnicki-Garcia, 2005 andMeyer et al, 2009). The RmsA gene is also present in the T. melanosporum genome and the alignment with the ortholog proteins of yeast and A. niger has allowed us to confirm the presence of the conserved domains.…”