Abstract
BackgroundLight represents an important environmental cue, which exerts considerable influence on the metabolism of fungi. Studies with the biotechnological fungal workhorse Trichoderma reesei (Hypocrea jecorina) have revealed an interconnection between transcriptional regulation of cellulolytic enzymes and the light response. Neurospora crassa has been used as a model organism to study light and circadian rhythm biology. We therefore investigated whether light also regulates transcriptional regulation of cellulolytic enzymes in N. crassa.ResultsWe show that the N. crassa photoreceptor genes wc-1, wc-2 and vvd are involved in regulation of cellulase gene expression, indicating that this phenomenon is conserved among filamentous fungi. The negative effect of VVD on production of cellulolytic enzymes is thereby accomplished by its role in photoadaptation and hence its function in White collar complex (WCC) formation. In contrast, the induction of vvd expression by the WCC does not seem to be crucial in this process. Additionally, we found that WC-1 and WC-2 not only act as a complex, but also have individual functions upon growth on cellulose.ConclusionsGenome wide transcriptome analysis of photoreceptor mutants and evaluation of results by analysis of mutant strains identified several candidate genes likely to play a role in light modulated cellulase gene expression. Genes with functions in amino acid metabolism, glycogen metabolism, energy supply and protein folding are enriched among genes with decreased expression levels in the wc-1 and wc-2 mutants. The ability to properly respond to amino acid starvation, i. e. up-regulation of the cross pathway control protein cpc-1, was found to be beneficial for cellulase gene expression. Our results further suggest a contribution of oxidative depolymerization of cellulose to plant cell wall degradation in N. crassa.
Highlights
Light represents an important environmental cue, which exerts considerable influence on the metabolism of fungi
We evaluate the phenotype of a number of mutants in genes that showed differential regulation in wc-1, wc-2 and vvd mutants as compared to wild type, revealing that these photoreceptors and the light response are involved in a complex adjustment of physiological processes and composition of the secreted enzyme mixture
Analysis of cellulolytic activity and growth of Δwc-1, Δwc2 and Δvvd mutants on cellulose Measurements of endoglucanase activity revealed that enzyme production is apparent after 16 hrs of growth when N. crassa is cultivated in liquid culture at 25°C with 2% (w/v) crystalline cellulose (Avicel) in light (Figure 1)
Summary
Light represents an important environmental cue, which exerts considerable influence on the metabolism of fungi. Neurospora crassa has been used as a model organism to study light and circadian rhythm biology. The filamentous fungus Neurospora crassa is one of the best studied organisms in this respect and has become a model system for understanding the light response and circadian rhythms [2,3,4,5]. Photoreceptors and their light responsive or neither light responsive nor circadian [17]. VVD was found to serve as a molecular memory of the brightness of the preceding day and to discriminate between high and low light, which is especially important for the correct reaction to moonlight [24]
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