Transcriptional Response of the Obligatory Aerobe Trichoderma reesei to Hypoxia and Transient Anoxia:  Implications for Energy Production and Survival in the Absence of Oxygen

Abstract

Oxygen is essential for the survival of obligatorily aerobic eukaryotic microorganisms, such as the multicellular fungus Trichoderma reesei. However, the molecular basis for the inability of such cells to survive for extended periods under anoxic conditions is not fully understood. Using cDNA microarray analysis, we show that changes in oxygen availability have a drastic effect on gene expression in T. reesei. The expression levels of 392 (19.6%) out of 2000 genes examined changed significantly in response to hypoxia, transient anoxia, and reoxygenation. In addition to modulating many genes with no previously assigned function, cells respond to hypoxia by readjusting the balance of expression between genes required for energy production and consumption, and altering the expression of genes involved in protective mechanisms and signaling pathways. Moreover, we show that transient anoxia strongly represses genes for enzymes that are critical for glycolysis, and are essential for energy production under anaerobic conditions. Our study thus reveals crucial differences between the facultative anaerobe Saccharomyces cerevisiae and T. reesei with regard to the oxygen-dependent transcriptional control of the glycolytic pathway, which can account for the differential survival of the two species in the absence of oxygen.

Expression of Biomass-Degrading Enzymes Is a Major Event during Conidium Development in Trichoderma reesei

“…Although such a finding has not been reported for either N. crassa or A. fumigatus (18,29), spores of the latter have been reported to perform fermentative metabolism (50), which is also reflected in an increased abundance of pyruvate decarboxylase and alcohol dehydrogenase in its conidia. We did not observe this for T. reesei, although it is capable of using pyruvate decarboxylase for fermentative metabolism at low oxygen concentrations (9). The downregulation of genes associated with mitochondrial functions may be a specific means to adapt to conditions of fermentative energy generation.…”

Transcriptional Response to Hypoxia in the Aquatic Fungus Blastocladiella emersonii

“…As stated above, B. emersonii cells subjected to hypoxia upregulate the expression of most genes encoding enzymes of the glycolytic pathway and the lactate dehydrogenase, differently from what is observed with the majority of TCA cycle enzyme genes, which were downregulated. In contrast, the most-important genes related to energetic metabolism did not seem to be significantly regulated during hypoxia in C. neoformans (9), and a drastic downregulation of most genes encoding glycolytic and TCA cycle enzymes was observed in T. reesei under hypoxia stress (5). Thus, the situation with these fungi is very distinct from what was found in B. emersonii, in which, at least transcriptionally, there is a metabolic shift to anaerobic fermentation.…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…The same gene was transferred in the biocontrol strain T. harzianum T34, which led to higher biomass production in the mutant strains than in the wildtype T34 strain and enhanced thermotolerance. The small heat shock protein HSP30 of T. reesei (TR_46285) and the heat shock protein HSP98 of the CLPA family were enhanced under hypoxic conditions and strongly induced under anaerobic conditions (986). HSP30 of N. crassa was shown not to be essential under high-temperature stress conditions but to be important for carbon utilization in high temperatures (987).…”