title: A putative DEAD-box RNA-helicase is required for normal zoospore development in the late blight pathogen Phytophthora infestans.
abstract: The asexual multinucleated sporangia of Phytophthora infestans can germinate directly through a germ tube or indirectly by releasing zoospores. The molecular mechanisms controlling sporangial cytokinesis or sporangial cleavage, and zoospore release are largely unknown. Sporangial cleavage is initiated by a cold shock that eventually compartmentalizes single nuclei within each zoospore. Comparison of EST representation in different cDNA libraries revealed a putative ATP-dependent DEAD-box RNA-helicase gene in P. infestans, Pi-RNH1, which has a 140-fold increased expression level in young zoospores compared to uncleaved sporangia. RNA interference was employed to determine the role of Pi-RNH1 in zoospore development. Silencing efficiencies of up to 99% were achieved in some transiently-silenced lines. These Pi-RNH1-silenced lines produced large aberrant zoospores that had undergone partial cleavage and often had multiple flagella on their surface. Transmission electron microscopy revealed that cytoplasmic vesicles fused in the silenced lines, resulting in the formation of large vesicles. The Pi-RNH1-silenced zoospores were also sensitive to osmotic pressure and often ruptured upon release from the sporangia. These findings indicate that Pi-RNH1 has a major function in zoospore development and its potential role in cytokinesis is discussed.
authors.affiliation: Aberdeen Oomycete Group, College of Life Science and Medicine, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK.
authors.forename: Claire A
authors.initials: CA
authors.lastname: Walker
authors.forename: Maico
authors.initials: M
authors.lastname: Köppe
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Grenville-Briggs
authors.forename: Anna O
authors.initials: AO
authors.lastname: Avrova
authors.forename: Neil R
authors.initials: NR
authors.lastname: Horner
authors.forename: Alastair D
authors.initials: AD
authors.lastname: McKinnon
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Whisson
authors.forename: Paul R J
authors.initials: PR
authors.lastname: Birch
authors.forename: Pieter
authors.initials: P
authors.lastname: van West
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010641:Phenotype; D010802:Phylogeny; D010838:Phytophthora / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D010935:Plant Diseases / Q000469:parasitology*; D034622:RNA Interference; D013170:Spores / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure
chemical_list: D020418:Algal Proteins; D053487:DEAD-box RNA Helicases