Membrane-Coupled mRNA Trafficking in Fungi

Abstract

Intracellular logistics are essential for delivery of newly synthesized material during polar growth of fungal hyphae. Proteins and lipids are actively transported throughout the cell by motor-dependent movement of small vesicles or larger units such as endosomes and the endoplasmic reticulum. A remarkably tight link is emerging between active membrane trafficking and mRNA transport, a process that determines the precise subcellular localization of translation products within the cell. Here, we report on recent insights into the mechanism and biological role of these intricate cotransport processes in fungal models such as Saccharomyces cerevisiae, Candida albicans, and Ustilago maydis. In the latter, we focus on the new finding of endosomal mRNA transport and its implications for protein targeting, complex assembly, and septin biology.

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

“…Importantly, both subcellular localizations of Cdc3 depend on Rrm4 (188). Since the presence of both cdc3 mRNA and ribosomes at early endosomes is dependent on Rrm4, the local translation of cdc3 mRNA most likely loads the cytoplasmic surface of endosomes with Cdc3 protein for transport toward the hyphal tip (161,188). Consistently, all four septin mRNAs and proteins localize to early endosomes and are assembled in higher-order filaments.…”

“…Endosomes serve as multipurpose platforms to transport a variety of cargo, such as lipids, proteins, mRNAs, ribosomes, and even whole organelles (160,161) (Fig. 5).…”

“…Alternatively, it was postulated that early endosomes might participate in signaling from the hyphal tip toward the nucleus to alter gene expression (169). However, studies of polar growth of infectious hyphae in U. maydis revealed novel and unexpected additional functions of endosomal transport (161).…”

When green and red mycology meet: Impressions from an interdisciplinary forum on virulence mechanisms of phyto- and human-pathogenic fungi

“…24,32 Also the UPR system as presented by Kai Heimel in his short talk on U. maydis has been recognized to support pathogenicity of human pathogenic fungi as well, 44,69 thereby representing a common determinant of fungal virulence. The same is obviously true for fungal-specific traits, such as RNA biology and transport elucidated by the Feldbr€ ugge group, 65 or the unique composition and structure of the fungal cell wall, as it has been studied by N. Gow and several others in the field. 70 An apparently more specific trait of plant-pathogenic fungi seems to be related to apoplastic effectors, 50,71 as they were presented by the IFoFun-2016 speakers A. Djamei and G. D€ ohlemann.…”

“…The expert in fungal RNA biology Michael Feldbr€ ugge from D€ usseldorf, Germany, gave an update on the RNA-binding protein Rrm4 of U. maydis and presented a regulator important for early endosome function in delivering de novo synthesized proteins together with endosomal mRNA. 65 In a concluding presentation, Neil Gow from Aberdeen, Scotland, spoke about the characteristics of the fungal cell wall to serve as immunological and drug target. He focused on N-mannan, which supports binding of human immune cells to C. albicans, and its synthesis that is mediated by a highly redundant gene family; 66 furthermore, he shared interesting data on the role of chitin in drug resistance and immune cell polarization.…”