scholarly journals Calcineurin and Calcium Channel CchA Coordinate the Salt Stress Response by Regulating Cytoplasmic Ca2+Homeostasis in Aspergillus nidulans

2016 ◽  
Vol 82 (11) ◽  
pp. 3420-3430 ◽  
Author(s):  
Sha Wang ◽  
Xiao Liu ◽  
Hui Qian ◽  
Shizhu Zhang ◽  
Ling Lu
Keyword(s):  
Salt Stress ◽  
Calcium Channel ◽  
Aspergillus Nidulans ◽  
Transient Receptor Potential ◽  
Feedback Inhibition ◽  
Calcium Influx ◽  
Hyphal Growth ◽  
Salt Stress Response ◽  
Content Type ◽  
Growth Defects

ABSTRACTThe eukaryotic calcium/calmodulin-dependent protein phosphatase calcineurin is crucial for the environmental adaption of fungi. However, the mechanism of coordinate regulation of the response to salt stress by calcineurin and the high-affinity calcium channel CchA in fungi is not well understood. Here we show that the deletion ofcchAsuppresses the hyphal growth defects caused by the loss of calcineurin under salt stress inAspergillus nidulans. Additionally, the hypersensitivity of the ΔcnaAstrain to extracellular calcium and cell-wall-damaging agents can be suppressed bycchAdeletion. Using the calcium-sensitive photoprotein aequorin to monitor the cytoplasmic Ca2+concentration ([Ca2+]c) in living cells, we found that calcineurin negatively regulates CchA on calcium uptake in response to external calcium in normally cultured cells. However, in salt-stress-pretreated cells, loss of eithercnaAorcchAsignificantly decreased the [Ca2+]c, but a deficiency in bothcnaAandcchAswitches the [Ca2+]cto the reference strain level, indicating that calcineurin and CchA synergistically coordinate calcium influx under salt stress. Moreover, real-time PCR results showed that the dysfunction ofcchAin the ΔcnaAstrain dramatically restored the expression ofenaA(a major determinant for sodium detoxification), which was abolished in the ΔcnaAstrain under salt stress. These results suggest that double deficiencies ofcnaAandcchAcould bypass the requirement of calcineurin to induceenaAexpression under salt stress. Finally, YvcA, a member of the transient receptor potential channel (TRPC) protein family of vacuolar Ca2+channels, was proven to compensate for calcineurin-CchA in fungal salt stress adaption.IMPORTANCEThe feedback inhibition relationship between calcineurin and the calcium channel Cch1/Mid1 has been well recognized from yeast. Interestingly, our previous study (S. Wang et al., PLoS One7:e46564, 2012,http://dx.doi.org/10.1371/journal.pone.0046564) showed that the deletion ofcchAcould suppress the hyphal growth defects caused by the loss of calcineurin under salt stress inAspergillus nidulans. In this study, our findings suggest that fungi are able to develop a unique mechanism for adapting to environmental salt stress. Compared to cells cultured normally, the NaCl-pretreated cells had a remarkable increase in transient [Ca2+]c. Furthermore, we show that calcineurin and CchA are required to modulate cellular calcium levels and synergistically coordinate calcium influx under salt stress. Finally, YvcA, a member of of the TRPC family of vacuolar Ca2+channels, was proven to compensate for calcineurin-CchA in fungal salt stress adaption. The findings in this study provide insights into the complex regulatory links between calcineurin and CchA to maintain cytoplasmic Ca2+homeostasis in response to different environments.

scholarly journals FigA, a Putative Homolog of Low-Affinity Calcium System Member Fig1 in Saccharomyces cerevisiae, Is Involved in Growth and Asexual and Sexual Development in Aspergillus nidulans

2013 ◽  
Vol 13 (2) ◽  
pp. 295-303 ◽  
Author(s):  
Shizhu Zhang ◽  
Hailin Zheng ◽  
Nanbiao Long ◽  
Natalia Carbó ◽  
Peiying Chen ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Aspergillus Nidulans ◽  
Sexual Development ◽  
Calcium Uptake ◽  
Fluorescent Protein ◽  
Calcium Influx ◽  
Hyphal Growth ◽  
Uptake System ◽  
Content Type ◽  
Green Fluorescent

ABSTRACTCalcium-mediated signaling pathways are widely employed in eukaryotes and are implicated in the regulation of diverse biological processes. InSaccharomyces cerevisiae, at least two different calcium uptake systems have been identified: the high-affinity calcium influx system (HACS) and the low-affinity calcium influx system (LACS). Compared to the HACS, the LACS in fungi is not well known. In this study, FigA, a homolog of the LACS member Fig1 fromS. cerevisiae, was functionally characterized in the filamentous fungusAspergillus nidulans. Loss offigAresulted in retardant hyphal growth and a sharp reduction of conidial production. Most importantly, FigA is essential for the homothallic mating (self-fertilization) process; further, FigA is required for heterothallic mating (outcrossing) in the absence of HACSmidA. Interestingly, in afigAdeletion mutant, adding extracellular Ca2+rescued the hyphal growth defects but could not restore asexual and sexual reproduction. Furthermore, quantitative PCR results revealed thatfigAdeletion sharply decreased the expression ofbrlAandnsdD, which are known as key regulators during asexual and sexual development, respectively. In addition, green fluorescent protein (GFP) tagging at the C terminus of FigA (FigA::GFP) showed that FigA localized to the center of the septum in mature hyphal cells, to the location between vesicles and metulae, and between the junctions of metulae and phialides in conidiophores. Thus, our findings suggest that FigA, apart from being a member of a calcium uptake system inA. nidulans, may play multiple unexplored roles during hyphal growth and asexual and sexual development.

scholarly journals Functional Analysis of Sterol Transporter Orthologues in the Filamentous Fungus Aspergillus nidulans

2015 ◽  
Vol 14 (9) ◽  
pp. 908-921 ◽  
Author(s):  
Nicole Bühler ◽  
Daisuke Hagiwara ◽  
Norio Takeshita
Keyword(s):  
Plasma Membrane ◽  
Aspergillus Nidulans ◽  
Filamentous Fungi ◽  
Gene Deletion ◽  
Fluorescent Protein ◽  
Fungal Growth ◽  
Hyphal Growth ◽  
Apical Plasma Membrane ◽  
Important Species ◽  
Content Type

ABSTRACT Polarized growth in filamentous fungi needs a continuous supply of proteins and lipids to the growing hyphal tip. One of the important membrane compounds in fungi is ergosterol. At the apical plasma membrane ergosterol accumulations, which are called sterol-rich plasma membrane domains (SRDs). The exact roles and formation mechanism of the SRDs remained unclear, although the importance has been recognized for hyphal growth. Transport of ergosterol to hyphal tips is thought to be important for the organization of the SRDs. Oxysterol binding proteins, which are conserved from yeast to human, are involved in nonvesicular sterol transport. In Saccharomyces cerevisiae seven oxysterol-binding protein homologues (OSH1 to -7) play a role in ergosterol distribution between closely located membranes independent of vesicle transport. We found five homologous genes ( oshA to oshE ) in the filamentous fungi Aspergillus nidulans . The functions of OshA-E were characterized by gene deletion and subcellular localization. Each gene-deletion strain showed characteristic phenotypes and different sensitivities to ergosterol-associated drugs. Green fluorescent protein-tagged Osh proteins showed specific localization in the late Golgi compartments, puncta associated with the endoplasmic reticulum, or diffusely in the cytoplasm. The genes expression and regulation were investigated in a medically important species Aspergillus fumigatus , as well as A. nidulans . Our results suggest that each Osh protein plays a role in ergosterol distribution at distinct sites and contributes to proper fungal growth.

scholarly journals Glutathione depletion activates the yeast vacuolar transient receptor potential channel, Yvc1p, by reversible glutathionylation of specific cysteines

2016 ◽  
Vol 27 (24) ◽  
pp. 3913-3925 ◽  
Author(s):  
Avinash Chandel ◽  
Krishna K. Das ◽  
Anand K. Bachhawat
Keyword(s):  
Calcium Channel ◽  
Transient Receptor Potential ◽  
Transmembrane Domain ◽  
Trp Channels ◽  
Calcium Influx ◽  
Receptor Potential ◽  
Transient Receptor Potential Channel ◽  
Glutathione Depletion ◽  
Glutathione S Transferase ◽  
Transient Receptor

Glutathione depletion and calcium influx into the cytoplasm are two hallmarks of apoptosis. We have been investigating how glutathione depletion leads to apoptosis in yeast. We show here that glutathione depletion in yeast leads to the activation of two cytoplasmically inward-facing channels: the plasma membrane, Cch1p, and the vacuolar calcium channel, Yvc1p. Deletion of these channels partially rescues cells from glutathione depletion–induced cell death. Subsequent investigations on the Yvc1p channel, a homologue of the mammalian TRP channels, revealed that the channel is activated by glutathionylation. Yvc1p has nine cysteine residues, of which eight are located in the cytoplasmic regions and one on the transmembrane domain. We show that three of these cysteines, Cys-17, Cys-79, and Cys-191, are specifically glutathionylated. Mutation of these cysteines to alanine leads to a loss in glutathionylation and a concomitant loss in calcium channel activity. We further investigated the mechanism of glutathionylation and demonstrate a role for the yeast glutathione S-transferase Gtt1p in glutathionylation. Yvc1p is also deglutathionylated, and this was found to be mediated by the yeast thioredoxin, Trx2p. A model for redox activation and deactivation of the yeast Yvc1p channel is presented.

scholarly journals Cryptic Aspergillus nidulans Antimicrobials

2011 ◽  
Vol 77 (11) ◽  
pp. 3669-3675 ◽  
Author(s):  
Steve S. Giles ◽  
Alexandra A. Soukup ◽  
Carrie Lauer ◽  
Mona Shaaban ◽  
Alexander Lin ◽  
...  
Keyword(s):  
Reactive Oxygen Species ◽  
Aspergillus Nidulans ◽  
Chromatin Remodeling ◽  
Fungal Pathogens ◽  
Reactive Oxygen Species Generation ◽  
Hyphal Growth ◽  
Gene Clusters ◽  
Oxygen Species ◽  
Content Type ◽  
Systematic Testing

ABSTRACTSecondary metabolite (SM) production by fungi is hypothesized to provide some fitness attribute for the producing organisms. However, most SM clusters are “silent” when fungi are grown in traditional laboratory settings, and it is difficult to ascertain any function or activity of these SM cluster products. Recently, the creation of a chromatin remodeling mutant inAspergillus nidulansinduced activation of several cryptic SM gene clusters. Systematic testing of nine purified metabolites from this mutant identified an emodin derivate with efficacy against both human fungal pathogens (inhibiting both spore germination and hyphal growth) and several bacteria. The ability of catalase to diminish this antimicrobial activity implicates reactive oxygen species generation, specifically, the generation of hydrogen peroxide, as the mechanism of emodin hydroxyl activity.

scholarly journals Protein Phosphatase 2A (PP2A) Regulatory Subunits ParA and PabA Orchestrate Septation and Conidiation and Are Essential for PP2A Activity in Aspergillus nidulans

2014 ◽  
Vol 13 (12) ◽  
pp. 1494-1506 ◽  
Author(s):  
Guo-wei Zhong ◽  
Ping Jiang ◽  
Wei-ran Qiao ◽  
Yuan-wei Zhang ◽  
Wen-fan Wei ◽  
...  
Keyword(s):  
Aspergillus Nidulans ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Hyphal Growth ◽  
Negative Regulator ◽  
Regulatory Subunit ◽  
Content Type ◽  
Regulatory Subunits ◽  
Pp2a Activity ◽  
Phosphatase 2A

ABSTRACTProtein phosphatase 2A (PP2A) is a major intracellular protein phosphatase that regulates multiple aspects of cell growth and metabolism. Different activities of PP2A and subcellular localization are determined by its regulatory subunits. Here we identified and characterized the functions of two protein phosphatase regulatory subunit homologs, ParA and PabA, inAspergillus nidulans. Our results demonstrate that ParA localizes to the septum site and that deletion ofparAcauses hyperseptation, while overexpression ofparAabolishes septum formation; this suggests that ParA may function as a negative regulator of septation. In comparison, PabA displays a clear colocalization pattern with 4′,6-diamidino-2-phenylindole (DAPI)-stained nuclei, and deletion ofpabAinduces a remarkable delayed-septation phenotype. BothparAandpabAare required for hyphal growth, conidiation, and self-fertilization, likely to maintain normal levels of PP2A activity. Most interestingly,parAdeletion is capable of suppressing septation defects inpabAmutants, suggesting that ParA counteracts PabA during the septation process. In contrast, double mutants ofparAandpabAled to synthetic defects in colony growth, indicating that ParA functions synthetically with PabA during hyphal growth. Moreover, unlike the case for PP2A-Par1 and PP2A-Pab1 in yeast (which are negative regulators that inactivate the septation initiation network [SIN]), loss of ParA or PabA fails to suppress defects of temperature-sensitive mutants of the SEPH kinase of the SIN. Thus, our findings support the previously unrealized evidence that the B-family subunits of PP2A have comprehensive functions as partners of heterotrimeric enzyme complexes of PP2A, both spatially and temporally, inA. nidulans.

scholarly journals Salt Stress Response of Sulfolobus acidocaldarius Involves Complex Trehalose Metabolism Utilizing a Novel Trehalose-6-Phosphate Synthase (TPS)/Trehalose-6-Phosphate Phosphatase (TPP) Pathway

2020 ◽  
Vol 86 (24) ◽  
Author(s):  
Christina Stracke ◽  
Benjamin H. Meyer ◽  
Anna Hagemann ◽  
Eunhye Jo ◽  
Areum Lee ◽  
...  
Keyword(s):  
Salt Stress ◽  
Stress Response ◽  
Extreme Environments ◽  
Compatible Solutes ◽  
Sulfolobus Acidocaldarius ◽  
Triple Mutant ◽  
Salt Stress Response ◽  
Content Type ◽  
Trehalose Metabolism

ABSTRACT The crenarchaeon Sulfolobus acidocaldarius has been described to synthesize trehalose via the maltooligosyltrehalose synthase (TreY) and maltooligosyltrehalose trehalohydrolase (TreZ) pathway, and the trehalose glycosyltransferring synthase (TreT) pathway has been predicted. Deletion mutant analysis of strains with single and double deletions of ΔtreY and ΔtreT in S. acidocaldarius revealed that in addition to these two pathways, a third, novel trehalose biosynthesis pathway is operative in vivo: the trehalose-6-phosphate (T6P) synthase/T6P phosphatase (TPS/TPP) pathway. In contrast to known TPS proteins, which belong to the GT20 family, the S. acidocaldarius TPS belongs to the GT4 family, establishing a new function within this group of enzymes. This novel GT4-like TPS was found to be present mainly in the Sulfolobales. The ΔtreY ΔtreT Δtps triple mutant of S. acidocaldarius, which lacks the ability to synthesize trehalose, showed no altered phenotype under standard conditions or heat stress but was unable to grow under salt stress. Accordingly, in the wild-type strain, a significant increase of intracellular trehalose formation was observed under salt stress. Quantitative real-time PCR showed a salt stress-mediated induction of all three trehalose-synthesizing pathways. This demonstrates that in Archaea, trehalose plays an essential role for growth under high-salt conditions. IMPORTANCE The metabolism and function of trehalose as a compatible solute in Archaea was not well understood. This combined genetic and enzymatic approach at the interface of microbiology, physiology, and microbial ecology gives important insights into survival under stress, adaptation to extreme environments, and the role of compatible solutes in Archaea. Here, we unraveled the complexity of trehalose metabolism, and we present a comprehensive study on trehalose function in stress response in S. acidocaldarius. This sheds light on the general microbiology and the fascinating metabolic repertoire of Archaea, involving many novel biocatalysts, such as glycosyltransferases, with great potential in biotechnology.

scholarly journals Aspergillus nidulans Ambient pH Signaling Does Not Require Endocytosis

2015 ◽  
Vol 14 (6) ◽  
pp. 545-553 ◽  
Author(s):  
Daniel Lucena-Agell ◽  
Antonio Galindo ◽  
Herbert N. Arst ◽  
Miguel A. Peñalva
Keyword(s):  
Plasma Membrane ◽  
Aspergillus Nidulans ◽  
Hyphal Growth ◽  
Proteolytic Processing ◽  
Current Evidence ◽  
Dependent Manner ◽  
Incomplete Block ◽  
Alkaline Ph ◽  
Content Type

ABSTRACT Aspergillus nidulans (Pal) ambient pH signaling takes place in cortical structures containing components of the ESCRT pathway, which are hijacked by the alkaline pH-activated, ubiquitin-modified version of the arrestin-like protein PalF and taken to the plasma membrane. There, ESCRTs scaffold the assembly of dedicated Pal proteins acting downstream. The molecular details of this pathway, which results in the two-step proteolytic processing of the transcription factor PacC, have received considerable attention due to the key role that it plays in fungal pathogenicity. While current evidence strongly indicates that the pH signaling role of ESCRT complexes is limited to plasma membrane-associated structures where PacC proteolysis would take place, the localization of the PalB protease, which almost certainly catalyzes the first and only pH-regulated proteolytic step, had not been investigated. In view of ESCRT participation, this formally leaves open the possibility that PalB activation requires endocytic internalization. As endocytosis is essential for hyphal growth, nonlethal endocytic mutations are predicted to cause an incomplete block. We used a SynA internalization assay to measure the extent to which any given mutation prevents endocytosis. We show that none of the tested mutations impairing endocytosis to different degrees, including slaB1 , conditionally causing a complete block, have any effect on the activation of the pathway. We further show that PalB, like PalA and PalC, localizes to cortical structures in an alkaline pH-dependent manner. Therefore, signaling through the Pal pathway does not involve endocytosis.

scholarly journals The Lectin Chaperone Calnexin Is Involved in the Endoplasmic Reticulum Stress Response by Regulating Ca2+ Homeostasis in Aspergillus nidulans

2017 ◽  
Vol 83 (15) ◽  
Author(s):  
Shenghua Zhang ◽  
Hailin Zheng ◽  
Qiuyi Chen ◽  
Yuan Chen ◽  
Sha Wang ◽  
...  
Keyword(s):  
Er Stress ◽  
Aspergillus Nidulans ◽  
Molecular Chaperone ◽  
Hyphal Growth ◽  
Extracellular Calcium ◽  
Free Calcium ◽  
Content Type ◽  
Free Calcium Concentration ◽  
Cytosolic Free Calcium Concentration ◽  
Limiting Condition

ABSTRACT The Ca2+-mediated signaling pathway is crucial for environmental adaptation in fungi. Here we show that calnexin, a molecular chaperone located in the endoplasmic reticulum (ER), plays an important role in regulating the cytosolic free calcium concentration ([Ca2+]c) in Aspergillus nidulans. Inactivation of calnexin (ClxA) in A. nidulans caused severe defects in hyphal growth and conidiation under ER stress caused by the ER stress-inducing agent dithiothreitol (DTT) or high temperature. Importantly, defects in the ΔclxA mutant were restored by the addition of extracellular calcium. Furthermore, the CchA/MidA complex (the high-affinity Ca2+ channels), calcineurin (calcium/calmodulin-dependent protein phosphatase), and PmrA (secretory pathway Ca2+ ATPase) were required for extracellular calcium-based restoration of the DTT/thermal stress sensitivity in the ΔclxA mutant. Interestingly, the ΔclxA mutant exhibited markedly reduced conidium formation and hyphal growth defects under the low-calcium condition, which is similar to defects caused by mutations in MidA/CchA. Moreover, the phenotypic defects were further exacerbated in the ΔclxA ΔmidA ΔcchA mutant, which suggested that ClxA and MidA/CchA are both required under the calcium-limiting condition. Using the calcium-sensitive photoprotein aequorin to monitor [Ca2+]c in living cells, we found that ClxA and MidA/CchA complex synergistically coordinate transient increase in [Ca2+]c in response to extracellular calcium. Moreover, ClxA, in particular its luminal domain, plays a role in mediating the transient [Ca2+]c in response to DTT-induced ER stress in the absence of extracellular calcium, indicating ClxA may mediate calcium release from internal calcium stores. Our findings provide new insights into the role of calnexin in the regulation of calcium-mediated response in fungal ER stress adaptation. IMPORTANCE Calnexin is a well-known molecular chaperone conserved from yeast to humans. Although it contains calcium binding domains, little is known about the role of calnexin in Ca2+ regulation. In this study, we demonstrate that calnexin (ClxA) in the filamentous fungus Aspergillus nidulans, similar to the high-affinity calcium uptake system (HACS), is required for normal growth and conidiation under the calcium-limiting condition. The ClxA dysfunction decreases the transient cytosolic free calcium concentration ([Ca2+]c) induced by a high extracellular calcium or DTT-induced ER stress. Our findings provide the direct evidence that calnexin plays important roles in regulating Ca2+ homeostasis in addition to its role as a molecular chaperone in fungi. These results provide new insights into the roles of calnexin and expand knowledge of fungal stress adaptation.

scholarly journals A Pericentrin-Related Protein Homolog in Aspergillus nidulans Plays Important Roles in Nucleus Positioning and Cell Polarity by Affecting Microtubule Organization

2012 ◽  
Vol 11 (12) ◽  
pp. 1520-1530 ◽  
Author(s):  
Peiying Chen ◽  
Rongsui Gao ◽  
Shaochun Chen ◽  
Li Pu ◽  
Pin Li ◽  
...  
Keyword(s):  
Aspergillus Nidulans ◽  
Coiled Coil ◽  
Related Protein ◽  
Microtubule Organization ◽  
Content Type ◽  
Growth Defects ◽  
Cytoskeletal Remodeling ◽  
Human Disorders ◽  
Related Proteins ◽  
Hyphal Apex

ABSTRACTPericentrin is a large coiled-coil protein in mammalian centrosomes that serves as a multifunctional scaffold for anchoring numerous proteins. Recent studies have linked numerous human disorders with mutated or elevated levels of pericentrin, suggesting unrecognized contributions of pericentrin-related proteins to the development of these disorders. In this study, we characterized AnPcpA, a putative homolog of pericentrin-related protein in the model filamentous fungusAspergillus nidulans, and found that it is essential for conidial germination and hyphal development. Compared to the hyphal apex localization pattern of calmodulin (CaM), which has been identified as an interactive partner of the pericentrin homolog, GFP-AnPcpA fluorescence dots are associated mainly with nuclei, while the accumulation of CaM at the hyphal apex depends on the function of AnPcpA. In addition, the depletion of AnPcpA by an induciblealcApromoter repression results in severe growth defects and abnormal nuclear segregation. Most interestingly, in mature hyphal cells, knockdown of pericentrin was able to significantly induce changes in cell shape and cytoskeletal remodeling; it resulted in some enlarged compartments with condensed nuclei and anucleate small compartments as well. Moreover, defects in AnPcpA significantly disrupted the microtubule organization and nucleation, suggesting that AnPcpA may affect nucleus positioning by influencing microtubule organization.

scholarly journals Endocytic Machinery Protein SlaB Is Dispensable for Polarity Establishment but Necessary for Polarity Maintenance in Hyphal Tip Cells of Aspergillus nidulans

2010 ◽  
Vol 9 (10) ◽  
pp. 1504-1518 ◽  
Author(s):  
América Hervás-Aguilar ◽  
Miguel A. Peñalva
Keyword(s):  
Plasma Membrane ◽  
Aspergillus Nidulans ◽  
Germ Tube ◽  
Fluorescent Protein ◽  
Hyphal Growth ◽  
Gene Replacement ◽  
Actin Binding ◽  
Nitrate Medium ◽  
Content Type ◽  
Tube Emergence

ABSTRACT The Aspergillus nidulans endocytic internalization protein SlaB is essential, in agreement with the key role in apical extension attributed to endocytosis. We constructed, by gene replacement, a nitrate-inducible, ammonium-repressible slaB1 allele for conditional SlaB expression. Video microscopy showed that repressed slaB1 cells are able to establish but unable to maintain a stable polarity axis, arresting growth with budding-yeast-like morphology shortly after initially normal germ tube emergence. Using green fluorescent protein (GFP)-tagged secretory v-SNARE SynA, which continuously recycles to the plasma membrane after being efficiently endocytosed, we establish that SlaB is crucial for endocytosis, although it is dispensable for the anterograde traffic of SynA and of the t-SNARE Pep12 to the plasma and vacuolar membrane, respectively. By confocal microscopy, repressed slaB1 germlings show deep plasma membrane invaginations. Ammonium-to-nitrate medium shift experiments demonstrated reversibility of the null polarity maintenance phenotype and correlation of normal apical extension with resumption of SynA endocytosis. In contrast, SlaB downregulation in hyphae that had progressed far beyond germ tube emergence led to marked polarity maintenance defects correlating with deficient SynA endocytosis. Thus, the strict correlation between abolishment of endocytosis and disability of polarity maintenance that we report here supports the view that hyphal growth requires coupling of secretion and endocytosis. However, downregulated slaB1 cells form F-actin clumps containing the actin-binding protein AbpA, and thus F-actin misregulation cannot be completely disregarded as a possible contributor to defective apical extension. Latrunculin B treatment of SlaB-downregulated tips reduced the formation of AbpA clumps without promoting growth and revealed the formation of cortical “comets” of AbpA.

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