Lipid and cell wall changes in an inositol-requiring mutant of Neurospora crassa

Abstract

An inositol deficiency in the inositol-requiring (inl) mutant of Neurospora crassa led to changes in the composition of the inositol-containing lipids and the cell wall. On deficient levels of inositol, phosphatidyl inositol decreased by 23fold, di(inositolphosphoryl) ceramide decreased by 4-fold, and monoinositolphosphoryl ceramide increased slightly. The inositol deficiency also led to an aberrant hyphal morphology and changes in both the amount of cell wall and the amino sugar content of the cell wall. The glucosamine content of the cell wall decreased by 50%, the galactosamine increased by 50%, but no significant changes were found in the content of the cell wall amino sugar precursors, or in the amino acid, glucose, or total hexose content of the cell wall. Inositol-containing compounds were found associated with purified cell wall material. These compounds were bound tightly to the cell wall but could be removed by treatment with alkali, a treatment which disrupts the cell wall integrity. Possible mechanisms of how changes in lipid composition can affect cell wall biosynthesis are discussed. 461 on July 16, 2020 by guest

Effects of inositol starvation on phospholipid and glycan syntheses in Saccharomyces cerevisiae

“…It would be interesting to know how the syntheses of these components are affected by inositol starvation. In Neurospora crassa, accumulation of chitin is affected by inositol starvation, whereas glucan accumulation is not (14). Roughly half of the inositol-containing lipid is sphingolipid (35).…”

Phospholipid requirements of membrane-bound chitin synthase from Absidia glauca

“…No other phospholipids such as PE, or PS had this effect, so PI, a common phospholipid in fungal membranes [11], plays a specific role in activating chitin synthase as found in S. commune [6]. It was demonstrated that the changes of the inositolcontaining lipids in the inl mutant of N. crassa led to an aberrant hyphal morphology and changes in the composition of the cell wall [3]. Under inositol starvation, S. cerevisiae [12] and the inl mutant of N. crassa exhibited a decrease in the content of acidic PI which was compensated by an increase in another acidic phospho- lipid, PS, and as a result the total phospholipid content and charge were conserved.…”

“…The inositol-requiring auxotrophic mutant of Neurospora crassa (inl) exhibits an aberrant hyphal morphology and changes in cell wall content [3] and these were caused by the extraordinary cell wall biosynthesis affected by the changes of membrane lipid composition. The Aspergillus nidulans choC mutant, which is unable to synthesize phosphatidylcholine (PC), demonstrated that membrane composition is an important determinant of both hyphal extension rate and mycelial morphology, and moreover, direct linear correlations were observed between PC content and in vivo chitin synthase activity [4].…”

Phase Resetting of the Neurospora crassa Circadian Oscillator: Effects of Inositol Depletion on Sensitivity to Light

“…If an inositol phospholipid signaling system is not directly involved in the light input pathway, there are a number of potential secondary effects of inositol depletion that might provide explanations for the increase in light sensitivity on low inositol. Inositol is incorporated into phospholipids and sphingolipids in Neurospora, but it is not incorporated into cell wall components (Hanson and Brody, 1979), and there are no reports of any other inositol-derived compounds in Neurospora. Effects of inositol depletion are therefore likely to be the direct or indirect results of changes in the levels of inositol-containing lipids.…”

“…A potentially important secondary effect of inositol depletion is that it has been shown to alter the phospholipid composition in Neurospora: As phosphatidylinositol decreases, phosphatidylserine increases (Hubbard and Brody, 1975;Gabrielides et al, 1983). Other changes in response to inositol depletion include increased lipid peroxidation and a decline in mitochondrial respiratory enzymes (Rana and Munkres, 1978), increased microviscosity of mitochondria (Munkres, 1979), and changes in inositol-containing sphingolipids (Hanson and Brody, 1979). If it is assumed that the photoreceptor and at least some of the components of the signaling pathway are membrane-bound, these changes in membrane properties could affect the sensitivity of the input pathway.…”