WHI-2 Regulates Intercellular Communication via a MAP Kinase Signaling Complex.

A Pedro Gonçalves,N Louise Glass,Karen M Chow,Sara Cea-Sánchez

doi:10.3389/fmicb.2019.03162

Abstract

The formation of the fungal mycelial network is facilitated by somatic cell fusion of germinating asexual spores (or germlings). Neurospora crassa germlings in close proximity display chemotropic growth that is dependent upon an intracellular network of mitogen-activated protein kinase (MAPK) signaling cascades. Approximately 80 genes involved in intercellular communication and fusion have been identified, including three mutants with similar morphological phenotypes: Δwhi-2, Δcsp-6, and Δamph-1. Here we show that WHI-2 localizes to the cell periphery and regulates endocytosis, mitochondrial organization, sporulation, and cell fusion. WHI-2 was required to transduce signals through a conserved MAPK pathway (NRC-1/MEK-2/MAK-2) and target transcription factors (PP-1/ADV-1). The amph-1 locus encodes a Bin/Amphiphysin/Rvs domain-containing protein and mis-expression of whi-2 compensated for the cell fusion and endocytosis deficiencies of a Δamph-1 mutant. The csp-6 locus encodes a haloacid dehalogenase phosphatase whose activity was essential for cell fusion. Although fusion-deficient with themselves, cells that lacked whi-2, csp-6, or amph-1 showed a low frequency of chemotropic interactions with wild type cells. We hypothesize that WHI-2 could be important for signal perception during chemotropic interactions via a role in endocytosis.

Highlights

Fungi can sense their surroundings, receive environmental cues, interpret them, and respond
Our study highlights the importance of WHI-2, an ortholog of the S. cerevisiae Whi2p, which binds to Psr1p (HAD family of protein phosphatases; CSP-6 ortholog) and regulates the response to nutritional stress by affecting both TORC1 and the Ras-cAMP-PKA pathway (Sudbery et al, 1980; Kaida et al, 2002; Müller and Reichert, 2011; Chen et al, 2018)
Using a constitutive nrc-1 allele, we showed that WHI-2 plays an active role during cell-cell communication in N. crassa by transducing signals to the NRC-1/MEK-2/MAK-2 pathway

Summary

INTRODUCTION

Fungi can sense their surroundings, receive environmental cues, interpret them, and respond . The tip recruitment and displacement of the MAK-2 signaling module to a single fusion tip occurs every ∼8–10 min and alternates at CAT and fusion tips of chemotropic partners in a perfectly out of phase manner with localization of SO, resembling a pingpong mechanism of signal sending and receiving (Fleissner et al, 2009b; Leeder et al, 2011; Serrano et al, 2018) These two pathways are required for the activation of the transcription factors PP-1 and ADV-1 that function as master regulators of cell fusion genes (Fischer et al, 2018). This work provides new details on genes/proteins that function upstream of a key MAPK signaling module

MATERIALS AND METHODS

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DISCUSSION

DATA AVAILABILITY STATEMENT