title: Rax2 is important for directional establishment of growth sites, but not for reorientation of growth axes, during Candida albicans hyphal morphogenesis.
abstract: Hyphae of filamentous fungi maintain generally linear growth over long distances. In Candida albicans, hyphae are able to reorient their growth in the direction of certain environmental cues. In previous work, the C. albicans bud-site selection proteins Rsr1 and Bud2 were identified as important for hyphae to maintain linear growth and were necessary for hyphal responses to directional cues in the environment (tropisms). To ask if hyphal directional responses are general functions of all yeast bud-site selection proteins, we studied the role of Rax2, ortholog of the Saccharomyces cerevisiae bud-site selection protein Rax2, in C. albicans hyphal morphogenesis. Rax2-YFP localized to the hyphal cell surface in puncta and at the hyphal tip in a crescent. Strains lacking Rax2 had hyphal morphologies that did not differ from control strains. In non-cued growth conditions, rax2 mutant strains had defects in both yeast (bud) and hyphal (branch) site selection and mutant hyphae exhibited non-linear growth trajectories as compared to control hyphae. In contrast, when encountering a directional environmental cue, hyphae lacking Rax2 retained the ability to reorient growth in response to both topographical (thigmotropism) and electric-field (galvanotropism) stimuli but exhibited a reduced ability to establish hyphal growth in the direction of a cathodal stimulus. In conclusion, these results indicate that C. albicans Rax2 is important for establishing sites of emergence of yeast and hyphal daughters and for maintaining the linearity of hyphal growth. In contrast to Rsr1 and Bud2, Rax2 is not involved in responses that require a reorientation of the direction of already established hyphal growth (tropisms). Thus, it appears that some hyphal directionality responses are separable in that they are mediated by a different set of polarity proteins.
authors.affiliation: Department of Pediatrics, University of Minnesota, MMC 391, 420 Delaware Street, SE, Minneapolis, MN 55455, USA. kegle015@umn.edu
authors.forename: Sara
authors.initials: S
authors.lastname: Gonia
authors.forename: Jennifer
authors.initials: J
authors.lastname: Norton
authors.forename: Lindy
authors.initials: L
authors.lastname: Watanaskul
authors.forename: Rebecca
authors.initials: R
authors.lastname: Pulver
authors.forename: Emma
authors.initials: E
authors.lastname: Morrison
authors.forename: Alexandra
authors.initials: A
authors.lastname: Brand
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Gale
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics; D002176:Candida albicans / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism*; D025301:Hyphae / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000235:genetics; D013194:Staining and Labeling; D018523:Tropism
chemical_list: D001426:Bacterial Proteins; D005656:Fungal Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C054562:yellow fluorescent protein, Bacteria