title: Polarized gene expression determines woronin body formation at the leading edge of the fungal colony.
abstract: The Woronin body (WB) is a peroxisome-related organelle that is centered on a crystalline core of the HEX-1 protein, which functions to seal septal pores of filamentous ascomycetes in response to cellular damage. Here, we investigate the cellular and genetic control of WB-formation and show that polarized hex-1 gene expression determines WB-biogenesis at the growing hyphal apex. We find that intron splicing is coupled to efficient hex-1 gene expression and strikingly, when the yellow fluorescent protein was expressed from hex-1 regulatory sequences, we observed a fluorescent gradient that was maximal in apical cells. Moreover, endogenous hex-1 transcripts were specifically enriched at the leading edge of the fungal colony, whereas other transcripts accumulated in basal regions. Time-lapse confocal microscopy showed that HEX-1 crystals normally formed in the vicinity of the hyphal apex in large peroxisomes, which matured and were immobilized at the cell periphery as cells underwent septation. When the hex-1 structural gene was expressed from regulatory sequences of an abundant, basally localized transcript, WB-core formation was redetermined to basal regions of the colony, and these strains displayed loss-of-function phenotypes specifically in apical hyphal compartments. These results show that apically localized gene expression is a key determinant of spatially restricted WB-assembly. We suggest that this type of regulation may be widely used to determine cellular activity in apical regions of the fungal hypha.
authors.affiliation: Comparative Cell Biology Group, Temasek Life Science Laboratory, National University of Singapore, Singapore 117604, Singapore.
authors.forename: Wei Kiat
authors.initials: WK
authors.lastname: Tey
authors.forename: Alison J
authors.initials: AJ
authors.lastname: North
authors.forename: Jose L
authors.initials: JL
authors.lastname: Reyes
authors.forename: Yan Fen
authors.initials: YF
authors.lastname: Lu
authors.forename: Gregory
authors.initials: G
authors.lastname: Jedd
mesh_terms: D016764:Cell Polarity; D005456:Fluorescent Dyes; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D025301:Hyphae / Q000166:cytology / Q000254:growth & development; D007438:Introns; D018613:Microscopy, Confocal; D018715:Microscopy, Video; D009492:Neurospora crassa / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D015388:Organelles / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020675:Peroxisomes / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D005456:Fluorescent Dyes; D005656:Fungal Proteins; C426803:Woronin body major protein, Neurospora crassa