title: Functional characterization of Rho GTPases in Aspergillus niger uncovers conserved and diverged roles of Rho proteins within filamentous fungi.
abstract: Rho GTPases are signalling molecules regulating morphology and multiple cellular functions including metabolism and vesicular trafficking. To understand the connection between polarized growth and secretion in the industrial model organism Aspergillus niger, we investigated the function of all Rho family members in this organism. We identified six Rho GTPases in its genome and used loss-of-function studies to dissect their functions. While RhoA is crucial for polarity establishment and viability, RhoB and RhoD ensure cell wall integrity and septum formation respectively. RhoC seems to be dispensable for A. niger. RacA governs polarity maintenance via controlling actin but not microtubule dynamics, which is consistent with its localization at the hyphal apex. Both deletion and dominant activation of RacA (Rac(G18V)) provoke an actin localization defect and thereby loss of polarized tip extension. Simultaneous deletion of RacA and CftA (Cdc42) is lethal; however, conditional overexpression of RacA in this strain can substitute for CftA, indicating that both proteins concertedly control actin dynamics. We finally identified NoxR as a RacA-specific effector, which however, is not important for apical dominance as reported for A. nidulans but for asexual development. Overall, the data show that individual Rho GTPases contribute differently to growth and morphogenesis within filamentous fungi.
authors.affiliation: Department Molecular Microbiology and Biotechnology, Institute of Biology Leiden, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands.
authors.forename: Min Jin
authors.initials: MJ
authors.lastname: Kwon
authors.forename: Mark
authors.initials: M
authors.lastname: Arentshorst
authors.forename: Eelke D
authors.initials: ED
authors.lastname: Roos
authors.forename: Cees A M J J
authors.initials: CA
authors.lastname: van den Hondel
authors.forename: Vera
authors.initials: V
authors.lastname: Meyer
authors.forename: Arthur F J
authors.initials: AF
authors.lastname: Ram
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005658:Fungi / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D025301:Hyphae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D008969:Molecular Sequence Data; D005810:Multigene Family; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D020741:rho GTP-Binding Proteins