Fungal hyphae extend by apical growth. This process involves the polarized traffic of secretory vesicles to the Spitzenkörper (SPK) and their subsequent distribution to specific domains of the plasma ...membrane, where they fuse to provide all the enzymes and material needed for cell wall expansion. Endocytic recycling and localized translation of specific mRNAs play an important role in hyphal apical growth. The traffic of vesicular carriers from synthesis sites to their destinations is coordinated by the combined action of coats, tethers, Rab GTPases, motors, and SNAREs in a mechanism that is just beginning to be understood. Only recently has it been confirmed that the different-sized vesicles present at the SPK contain distinct cell wall biosynthetic activities and are distributed in a stratified manner.
Filamentous fungi constitute a large group of eukaryotic microorganisms that grow by forming simple tube-like hyphae that are capable of differentiating into more-complex morphological structures and ...distinct cell types. Hyphae form filamentous networks by extending at their tips while branching in subapical regions. Rapid tip elongation requires massive membrane insertion and extension of the rigid chitin-containing cell wall. This process is sustained by a continuous flow of secretory vesicles that depends on the coordinated action of the microtubule and actin cytoskeletons and the corresponding motors and associated proteins. Vesicles transport cell wall-synthesizing enzymes and accumulate in a special structure, the Spitzenkörper, before traveling further and fusing with the tip membrane. The place of vesicle fusion and growth direction are enabled and defined by the position of the Spitzenkörper, the so-called cell end markers, and other proteins involved in the exocytic process. Also important for tip extension is membrane recycling by endocytosis via early endosomes, which function as multipurpose transport vehicles for mRNA, septins, ribosomes, and peroxisomes. Cell integrity, hyphal branching, and morphogenesis are all processes that are largely dependent on vesicle and cytoskeleton dynamics. When hyphae differentiate structures for asexual or sexual reproduction or to mediate interspecies interactions, the hyphal basic cellular machinery may be reprogrammed through the synthesis of new proteins and/or the modification of protein activity. Although some transcriptional networks involved in such reprogramming of hyphae are well studied in several model filamentous fungi, clear connections between these networks and known determinants of hyphal morphogenesis are yet to be established.
The deep sea (>1000 m below sea level) represents one of the most extreme environments of the ocean. Despite exhibiting harsh abiotic conditions such as low temperatures, high hydrostatic pressure, ...high salinity concentrations, a low input of organic matter, and absence of light, the deep sea encompasses a great fungal diversity. For decades, most knowledge on the fungal diversity of the deep sea was obtained through culture-dependent techniques. More recently, with the latest advances of high-throughput next generation sequencing platforms, there has been a rapid increment in the number of studies using culture-independent techniques. This review brings into the spotlight the progress of the techniques used to assess the diversity and ecological role of the deep-sea mycobiota and provides an overview on how the omics technologies have contributed to gaining knowledge about fungi and their activity in poorly explored marine environments. Finally, current challenges and suggested coordinated efforts to overcome them are discussed.
Tip-growing fungal cells maintain cell polarity at the apical regions and elongate by
synthesis of the cell wall. Cell polarity and tip growth rate affect mycelial morphology. However, it remains ...unclear how both features act cooperatively to determine cell shape. Here, we investigated this relationship by analyzing hyphal tip growth of filamentous fungi growing inside extremely narrow 1 μm-width channels of microfluidic devices. Since the channels are much narrower than the diameter of hyphae, any hypha growing through the channel must adapt its morphology. Live-cell imaging analyses revealed that hyphae of some species continued growing through the channels, whereas hyphae of other species often ceased growing when passing through the channels, or had lost apical polarity after emerging from the other end of the channel. Fluorescence live-cell imaging analyses of the Spitzenkörper, a collection of secretory vesicles and polarity-related proteins at the hyphal tip, in
indicates that hyphal tip growth requires a very delicate balance of ordered exocytosis to maintain polarity in spatially confined environments. We analyzed the mycelial growth of seven fungal species from different lineages, including phytopathogenic fungi. This comparative approach revealed that the growth defects induced by the channels were not correlated with their taxonomic classification or with the width of hyphae, but, rather, correlated with the hyphal elongation rate. This report indicates a trade-off between morphological plasticity and velocity in mycelial growth and serves to help understand fungal invasive growth into substrates or plant/animal cells, with direct impact on fungal biotechnology, ecology, and pathogenicity.
Cell morphology, which is controlled by polarity and growth, is fundamental for all cellular functions. However how polarity and growth act cooperatively to control cell shape remains unclear. Here we investigated their relationship by analyzing hyphal tip growth of filamentous fungi growing inside extremely narrow 1 μm-width channels of microfluidic devices. We found that most fast growing hyphae often lost the cell polarity after emerging from the channels, whereas slow growing hyphae retained polarity and continued growing, indicating a trade-off between plasticity and velocity in mycelial growth. These results serve to understand fungal invasive growth into substrates or plant/animal cells, with direct impact on fungal biotechnology, ecology and pathogenicity.
Hyphae represent a hallmark structure of multicellular fungi. The evolutionary origins of hyphae and of the underlying genes are, however, hardly known. By systematically analyzing 72 complete ...genomes, we here show that hyphae evolved early in fungal evolution probably via diverse genetic changes, including co-option and exaptation of ancient eukaryotic (e.g. phagocytosis-related) genes, the origin of new gene families, gene duplications and alterations of gene structure, among others. Contrary to most multicellular lineages, the origin of filamentous fungi did not correlate with expansions of kinases, receptors or adhesive proteins. Co-option was probably the dominant mechanism for recruiting genes for hypha morphogenesis, while gene duplication was apparently less prevalent, except in transcriptional regulators and cell wall - related genes. We identified 414 novel gene families that show correlated evolution with hyphae and that may have contributed to its evolution. Our results suggest that hyphae represent a unique multicellular organization that evolved by limited fungal-specific innovations and gene duplication but pervasive co-option and modification of ancient eukaryotic functions.
GS-1 (ncu04189) is a protein required for the synthesis of β-1,3-glucan in Neurospora crassa. As chitin, β-1,3-glucan is a morphogenetically relevant component of the fungal cell wall. Previously, we ...showed that chitin synthases are delivered to the growing hyphal tip of N. crassa by secretory microvesicles that follow an unconventional route and accumulate in the core of the Spitzenkörper (Spk). Tagged with the green fluorescent protein (GFP), GS-1 accumulated in the hyphal apex forming a dynamic and pleomorphic ring-like structure ('Spitzenring') that corresponded to the Spk outer macrovesicular stratum and surrounded the inner core of chitin synthase-containing microvesicles. TIRF microscopy revealed that GS-1-GFP reached the hyphal apex as a population of heterogeneous-size particles that moved along defined paths. On sucrose density gradients, GS-1-associated particles mainly sedimented in a high density range 1.1272-1.2124 g ml⁻¹. Clearly, GS-1 and chitin synthases of N. crassa are contained in two different types of secretory vesicles that accumulate in different strata of the Spk, a differentiation presumably related to the spatial control of cell-wall synthesis.
Summary
Fungi from marine environments have been significantly less studied than terrestrial fungi. This study describes distribution patterns and associated habitat characteristics of the mycobiota ...of deep‐sea sediments collected from the Mexican exclusive economic zone (EEZ) of the Gulf of Mexico (GoM), ranging between 1000 and > 3500 m depth. Internal Transcribed Spacer 1 (ITS1) amplicons were sequenced by Illumina MiSeq. From 29 stations sampled across three annual campaigns, a total of 4421 operational taxonomic units (OTUs) were obtained, indicating a high fungal richness. Most OTUs assignments corresponded to Ascomycota, unidentified fungi and Basidiomycota. The majority of the stations shared a mere 31 OTUs, including the worldwide reported genera Penicillium, Rhodotorula and Cladosporium. Both a transient and a conserved community were identified, suggesting their dependence on or adaptation to the habitat dynamics, respectively. The differences found in fungal richness and taxonomic compositions were correlated principally with latitude, carbon and carbonates content, and terrigenous content, which could be the potential drivers that delimit fungal distribution. This study represents an expansion of our current knowledge on the biogeography of the fungal community from deep‐sea sediments, and identifies the geographic and physicochemical properties that delimit fungal composition and distribution in the GoM.
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•Role of glycoside hydrolases BGT-1 and BGT-2 from GH-17 in Neurospora crassa.•GFP-tagging strategy for secreted proteins with a GPI anchor.•BGT-1 and BGT-2 localization at cell wall ...remodeling sites.•Prominent role of BGT-1 and BGT-2 in conidial separation.•Proposal for an integrative model of action for BGT-1 and BGT-2.
Neurospora crassa BGT-1 (NCU06381) and BGT-2 (NCU09175) are two putative glycoside hydrolases (GHs) with additional predicted glycosyltransferase activity and binding sites for a glycosyl phosphatidyl inositol (GPI) anchor that would facilitate their attachment to the plasma membrane (PM). To discern their role in key morphogenetic events during vegetative development of N. crassa, BGT-1 and BGT-2 were labeled with the green fluorescent protein (GFP). The gfp was inserted immediately after the signal peptide sequence, within the bgt-1 encoding sequence, or directly before the GPI-binding site in the case of bgt-2. Both BGT-1-GFP and BGT-2-GFP were observed at the PM of the hyphal apical dome, excluding the foremost apical region and the Spitzenkörper (Spk), where chitin and β-1,3-glucan synthases have been previously found. These and previous studies suggest a division of labor of the cell wall synthesizing machinery at the hyphal dome: at the very tip, glucans are synthesized by enzymes that accumulate at the Spk, before getting incorporated into the PM, whereas at the subtending zone below the apex, glucans are presumably hydrolyzed, producing amenable ends for further branching and crosslinking with other cell wall polymers. Additionally, BGT-1-GFP and BGT-2-GFP were observed at the leading edge of new developing septa, at unreleased interconidial junctions, at conidial poles, at germling and hyphal fusion sites, and at sites of branch emergence, all of them processes that seemingly involve cell wall remodeling. Even though single and double mutant strains for the corresponding genes did not show a drastic reduction of growth rate, bgt-2Δ and bgt-1Δ::bgt-2Δ strains exhibited an increased resistance to the cell wall stressors calcofluor white (CW) and congo red (CR) than the reference strain, which suggests they present significant architectural changes in their cell wall. Furthermore, the conidiation defects observed in the mutants indicate a significant role of BGT-1 and BGT-2 on the re-arrangement of glucans needed at the conidiophore cell wall to allow conidial separation.
Filamentous fungi are a large and ancient clade of microorganisms that occupy a broad range of ecological niches. The success of filamentous fungi is largely due to their elongate hypha, a chain of ...cells, separated from each other by septa. Hyphae grow by polarized exocytosis at the apex, which allows the fungus to overcome long distances and invade many substrates, including soils and host tissues. Hyphal tip growth is initiated by establishment of a growth site and the subsequent maintenance of the growth axis, with transport of growth supplies, including membranes and proteins, delivered by motors along the cytoskeleton to the hyphal apex. Among the enzymes delivered are cell wall synthases that are exocytosed for local synthesis of the extracellular cell wall. Exocytosis is opposed by endocytic uptake of soluble and membrane-bound material into the cell. The first intracellular compartment in the endocytic pathway is the early endosomes, which emerge to perform essential additional functions as spatial organizers of the hyphal cell. Individual compartments within septated hyphae can communicate with each other via septal pores, which allow passage of cytoplasm or organelles to help differentiation within the mycelium. This article introduces the reader to more detailed aspects of hyphal growth in fungi.
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