Age-dependent differential responses ofSaprolegnia hyphal tips to a helical growth-inducing factor in the agar substitute,gellan |
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| Institution: | 1. Department of Cardiology, State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China;2. Department of Pathology, State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China;3. McKusick–Zhang Center for Genetic Medicine, National Key Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China;1. School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia;2. Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom;3. Fish Health Laboratory, Department of Fisheries Western Australia, 3 Baron-Hay Court, South Perth, Western Australia 6151, Australia;4. Centre for Sustainable Tropical Fisheries and Aquaculture, College of Marine and Environmental Sciences, James Cook University, Cairns, Queensland 4878, Australia;5. The Faculty of Veterinary Medicine, Sudirman Campus, Universitas Udayana, Jalan Kampus Udayana, Denpasar 80361, Indonesia;6. Faculty of Agricultural and Environmental Sciences, Aquaculture and Sea-ranching, University Rostock, Justus-von-Liebig Weg 6, 18059 Rostock, Germany |
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| Abstract: | Saprolegnia ferax produces more-or-less straight, subapically branched, hyphae when growing in liquid or agar-solidified media, with abundant aerial mycelium on the latter. In Contrast, the same medium solidified with gellan gum induced helical growth with reduced branching and almost no aerial mycelium. Helical growth induction was gellan concentration-dependent, peaking at 0.4–0.6% (w/v), when about 60% of tips were helical. Gellan-induced helices showed concentration-dependent inhibition by agarose and polyethylene glycol. Colonies on gellan-agarose, where helices were inhibited, reverted to having aerial mycelium, whereas those on gellan-polyethylene glycol did not. Branches on helical hyphae were initially linear, but converted to helical growth after about 2 h of extension. This transition was often marked by a branch, thus branch and helix competency appeared to be related. Germinating cysts took twice as long as hyphal inocula before producing helical hyphae, reinforcing the suggestion that helix competence was age-related.Achlya, but notPhytophthora, also showed gellan-induced helical growth and aerial mycelium suppression. These results showed (a) that morphogenic regulators of hyphal growth responded to gelling agents, probably high-molecular-weight polysaccharides, (b) that all growing hyphal tips were not equivalent, and (c) that hyphal tips underwent age-related changes in their response to the environment. The gellan-related differences in aerial mycelium mimic hydrophobin-based mycelium behavior and may thus indicate environmental regulation of hydrophobin production. |
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