A network of MAP-Kinase pathways and transcription factors regulates cell-to-cell communication and cell wall integrity in Neurospora crassa

Abstract

Maintenance of cell integrity and cell-to-cell communication are fundamental biological processes. Filamentous fungi, such as Neurospora crassa, depend on communication to locate compatible cells, coordinate cell fusion, and establish a robust hyphal network. Two MAP-Kinase pathways are essential for communication and cell fusion in N. crassa; the Cell Wall Integrity/MAK-1 pathway and the MAK-2 (signal response) pathway. Previous studies have demonstrated several points of cross talk between the MAK-1 and MAK-2 pathways, which is likely necessary for oordinating chemotropic growth toward an extracellular signal, and then mediating cell fusion. Canonical MAP-Kinase pathways begin with signal reception and end with a transcriptional response. Two transcription factors, ADV-1 and PP-1, are essential for communication and cell fusion. PP-1 is the conserved target of MAK-2, while it is unclear what targets ADV-1. We did RNAseq on{Delta} adv-1, {Delta}pp-1, and wild-type cells and found that ADV-1 and PP-1 have a shared regulon including many genes required for communication, cell fusion, growth, development, and stress response. We identified ADV-1 and PP-1 binding sites across the genome by adapting the in vitro method of DNA-Affinity Purification sequencing (DAP-seq) for N. crassa. To elucidate the regulatory network, we misexpressed each transcription factor in each upstream MAPK deletion mutant. Misexpression of adv-1 was sufficient to fully suppress the phenotype of the{Delta} pp-1 mutant and partially suppress the phenotype of the{Delta} mak-1 mutant. Collectively, our data demonstrate that the MAK-1-ADV-1 and MAK-2- PP-1 pathways form a tight regulatory network that maintains cell integrity and mediates communication and cell fusion.