Biogenesis of Mitochondrial Membranes in Neurospora crassa

Abstract

The conidia of Neurospora crassa entered logarithmic growth after a 1‐h lag period at 30°C. Although [14C]leucine is incorporated quickly early in growth, cellular protein data indicated that no net protein synthesis occurred until after 2 h of growth. Neurospora is known to produce ethanol during germination even though respiratory enzymes are present. Also, Neurospora mitochondria isolated from cells less than 3‐h old are uncoupled. Since oxygen uptake increased during germination, was largely cyanide‐sensitive, and reached a maximum at 3 h, it is hypothesized that during early germination the uncoupled electron transport chain merely functions to dispose of reducing equivalents generated by substrate level ATP production. The rate of protein synthesis in vitro by mitochondria isolated from 0–8‐h‐old cells increased as did cell age. Mitochondrial protein synthesis in vivo, assayed in the presence of 100 μg cycloheximide/ml, increased from low levels in the conidia to peak levels at 3–4 h of age and then slowly decreased. The rate of mitochondrial protein synthesis in vivo was linear for at least 90 min in 0–4‐h‐old cells, but declined after 15 min of incorporation in 6 and 8‐h‐old cells. The products of mitochondrial protein synthesis in vivo were analyzed with dodecylsulfate gel electrophoresis and autoradiography. Early in germination 80% of the synthesis was of two small proteins (molecular weights 7200 and 9000). At 8 h 85% of the radioactivity was in 10 larger proteins (12200 to 80000). Within the high‐molecular‐weight class, proteins of between 12000 and 21500 molecular weight were preferentially labelled early in germination, whereas after 8 h of growth proteins of 27500 to 80000 molecular weight were preferentially labelled. It is hypothesized that the 7200 and 9000‐molecular‐weight products of mitochondrial protein synthesis combine with other proteins to form the larger proteins found later in growth. The availability of these other proteins in cells of different ages could affect the rate of mitochondrial protein synthesis in vivo.

Asp f6, an Aspergillus allergen specifically recognized by IgE from patients with allergic bronchopulmonary aspergillosis, is differentially expressed during germination

“…unpublished data). Further evidence that fermentation, but not respiration, is essential for germination of filamentous fungi has been provided for N. crassa (15).…”

Nutrient transport into germinating Trichoderma atroviride conidia and development of its driving force

“…Knowledge of the mechanisms underlying genetic and metabolic changes during spore germination in several fungal species has largely come in recent decades, including osmolyte metabolism (d 'Enfert et al, 1999;Döhlemann et al, 2006), protein synthesis (Leng et al, 2008;Oh et al, 2010;El-Akhal et al, 2013), changes of gene expression (Liu et al, 2007;Lamarre et al, 2008;Novodvorska et al, 2013;van Leeuwen et al, 2013) or involvement of signalling pathways (Osherov & May, 2001;d'Enfert, 1997;Mukherjee et al, 2007;Eaton et al, 2012 Metabolism of dormant conidia lacks respiratory activity and may be supported by fermentative metabolism (Teutschbein et al, 2010). Their germination is accompanied by the onset of cytochrome c oxidase biosynthesis (Hawley & Greenawalt, 1975;Brambl, 1980;Stade & Brambl, 1981) and of respiration (Chovanec et al, 2005;Nižň anský et al, 2013), the latter being indispensable for germination (Liu et al, 2007;Taubitz et al, 2007).…”