Abstract
Filamentous fungi are the main source of enzymes used to degrade lignocellulose to fermentable sugars for the production of biofuels. While the most commonly used organism for the production of cellulases in an industrial setting is Trichoderma reesei (Hypocrea jecorina), recent work in the model filamentous fungus Neurospora crassa has shown that the variety of molecular, genetic and biochemical techniques developed for this organism can expedite analyses of the complexities involved in the utilization of lignocellulose as a source of carbon. These include elucidating regulatory networks associated with plant cell wall deconstruction, the identification of signaling molecules necessary for induction of the expression of genes encoding lignocellulolytic enzymes and the characterization of new cellulolytic enzymatic activities. In particular, the availability of a full genome deletion strain set for N. crassa has expedited high throughput screening for mutants that display a cellulolytic phenotype. This review summarizes the key findings of several recent studies using N. crassa to further understanding the mechanisms of plant cell wall deconstruction by filamentous fungi.
Highlights
Every year photosynthesis converts approximately 100 billion metric tons of CO2 and H2O into cellulose [1]
Concluding remarks Historically, work on lignocellulose degrading filamentous fungi has primarily focused on T. reesei because of its importance in industry and many of these studies have focused on improving the enzyme yield when growing under industrially relevant conditions
Our understanding of the interwoven regulatory networks associated with plant cell wall deconstruction, transport and other enzymatic functions is still fragmented, as is how lignocellulose degrading filamentous fungi adapt and respond to a rapidly changing environment during plant biomass deconstruction
Summary
Every year photosynthesis converts approximately 100 billion metric tons of CO2 and H2O into cellulose [1]. In addition to CLR-1 and CLR-2, N. crassa contains a homolog of xlnR (xlr-1), another transcription factor involved in growth on lignocellulosic biomass While work in both N. crassa [32] and Fusarium [34,35] species indicates that the genes regulated by XLR-1/ XlnR are limited to those required to degrade xylan, in T. reesei and Aspergillus species, XYR1/XlnR regulates the expression of both cellulase and hemicellulose genes [36,37,38]. The work in N. crassa was aided by the availability of gene deletion strains and genetic/expression tools that aided purification and characterization of the PMOs. While the specific catalytic mechanism is the subject of current research (see [46]), initial data suggests that in nature GH61 enzymes may receive electrons from the action of cellobiose dehydrogenase (CDH) [47], which makes up 2.4% of the N. crassa culture cellulose secretome by weight.
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