Phosphoinositides Play a Role in Hyphal Extension and Branching in Neurospora crassa

Hosking, S. L., Robson, G. D., and Trinci, A. P. J. 1995. Phosphoinositides play a role in hyphal extension and branching in Neurospora crassa. Experimental Mycology 19, 71-80. Three phosphoinositide turnover inhibitors, lysocellin (8 μM), piericidin B₁N -oxide (11 μM), and (2S, 3R, 5R)-3-azido-2-benzoyloxy-5-hydroxycyclohexanone, an inositol analogue (8 μM), were found to act as paramorphogens, inhibiting hyphal extension and increasing hyphal branching of Neurospora crassa without affecting specific growth rate. At higher concentrations (lysocellin, 50 μM; piericidin B₁N-oxide, 500 μM; inositol analogue, 50 μM) the compounds inhibited spore germination. At 1.6 μM, lysocellin reduced the level of phosphatidylinositol phosphate and phosphatidylinositol bisphosphate in N. crassa by 65 and 90%, respectively. The site of action of lysocellin was shown to be phosphatidylinositol kinase. At 1.3 μM, lysocellin completely inhibited phosphatidylinositol kinase activity in vitro, a figure comparable to the concentration at which it inhibits phosphoinositide turnover in mammalian cells.