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Genome-wide analysis of the endoplasmic reticulum stress response during lignocellulase production in Neurospora crassa.

ABSTRACT: BACKGROUND:Lignocellulolytic fungal cells suffer endoplasmic reticulum (ER) stress during lignocellulase synthesis; however, an understanding of this integrated process on a genome-wide scale remains poor. Here, we undertook a systematic investigation of this process in Neurospora crassa (N. crassa) using transcriptomic analysis coupled with genetic screens. RESULTS:A set of 766 genes was identified as the ER stress response targets (ESRTs) in N. crassa under cellulose utilization conditions. Among these, the expression of 223 and 186 genes showed dependence on IRE-1 and HAC-1, respectively. A total of 527 available mutants for ESRT genes were screened, 249 of which exhibited ER stress susceptibility, including 100 genes with unknown function. Disruption of ire-1 or hac-1 in N. crassa did not affect transcriptional induction of lignocellulase genes by cellulose but severely affected secretion of the corresponding enzymes. A global investigation of transcription factors (TFs) discovered three novel regulators (RES-1, RES-2, RRG-2) involved in lignocellulase secretion. Production of lignocellulases in Δres-1 increased by more than 30% in comparison to wild type (WT), while secretion decreased by nearly 30% in strains Δres-2 and Δrrg-2. Transcriptional profiling of the three TF mutants suggests they are deeply involved in lignocellulase secretion and ER stress response. CONCLUSIONS:Here, we determined the transcriptional scope of the ER stress response during lignocellulase synthesis in the model cellulolytic fungus N. crassa. Through genome-wide mutant screening and analysis, dozens of novel genes were discovered to be involved in the process. The findings of this work will be useful for strain improvement to facilitate lignocellulase and biomass-based chemical production.

SUBMITTER: Fan F

PROVIDER: S-EPMC4399147 | biostudies-other | 2015

REPOSITORIES: biostudies-other

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Genome-wide analysis of the endoplasmic reticulum stress response during lignocellulase production in Neurospora crassa.

Fan Feiyu F Ma Guoli G Li Jingen J Liu Qian Q Benz Johan Philipp JP Tian Chaoguang C Ma Yanhe Y

Biotechnology for biofuels 20150414

<h4>Background</h4>Lignocellulolytic fungal cells suffer endoplasmic reticulum (ER) stress during lignocellulase synthesis; however, an understanding of this integrated process on a genome-wide scale remains poor. Here, we undertook a systematic investigation of this process in Neurospora crassa (N. crassa) using transcriptomic analysis coupled with genetic screens.<h4>Results</h4>A set of 766 genes was identified as the ER stress response targets (ESRTs) in N. crassa under cellulose utilization ...[more]

PMID: 25883682

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Project description:Purpose: To explore the pathway cross-talk of endoplasmic reticulum (ER) stress response and cellulases synthesis in Neurospora crassa. Methods: To identify ER stress response targets(ESRTs), conidial suspensions of WT were obtained and 1 x 10^6 cells/ml incubated in cellulases induction medium (1x vogel’s salts , 1% w/v crystalline cellulose (Avicel PH-101; Sigma-Aldrich), 0.2% w/v NH4NO3 ,pH 7.0 )for 36 hours (25ºC, 200 rpm, constant light) followed by the addition of dithiothreitol (DTT, final concentration of 0.1mM for mild stress level while 5mM for acute stress level) or tunicamycin (TM, final concentration of 5ug/mL for mild stress level while 40ug/mL for acute stress level) and growth for 1 more hour.To identify which ESRTs regulated by IRE-1/Hac-1 mediated UPR pathway,conidial suspensions of the Ire-1 and Hac-1 KO mutants as well as their parental strains (FGSC#2489 and FGSC#9720, respectively) were obtained and 1 x 10^6 cells/ml incubated in minimal medium containing 2% sucrose for 16 hours, then young hyphae was harvested and transferred into cellulases induction medium as mentioned above culture for 4 hours followed by the addition of DTT (final concentration of 5mM)(or H2O as mock)and growth for 1 more hour.For Hac-1 KO mutant and FGSC#9720,cultures were plus with final concentration of 100ug/ml L-histidine.To explore the function of transcription factors RES-1, RES-2 and RRG-2 in response to ER stress and cellulases synthesis, each conidial suspension of the three strains was obtained and 1 x 10^6 cells/ml incubated in cellulases induction medium for 36 hours followed by the addition of dithiothreitol (DTT, final concentration of 5mM ) (or H2O as mock)and growth for 1 more hour.Cells were harvested by vacuum filtration with Whatman filter paper, frozen immediately in liquid nitrogen. Total RNA was isolated by the Trizol-Phenol-Chloroform method. An additional clean-up including the on-column DNase I treatment was performed by using the RNeasy mini kit (Qiagen).The thirteen 49-nt single-end RNA-seq libraries were generated commercially at Beijing Genomics Institute (BGI, Shenzhen, China) while eight 90-nt paired-end RNA-seq libraries were generated at Genewiz Co. Ltd (Suzhou) by using the HiSeq™ platform.Sequencing data was handled essentially with Bowtie2, Tophat2, NOIseq. Expression levels are presented as Reads Per Kilobase of transcript per Million mapped reads (RPKM). Results: Transcriptional profiling of ER stress during cellulase synthesis in N.crassa uncovered a set of 766 genes was identified as the ER stress response target genes (ESRTs). Of these 766 genes, canonical UPR components IRE-1 and HAC-1 regulated 223 and 186 genes, respectively. In screening 527 available ESRT mutants, we found 249 that exhibited DTT sensibility, including 100 targets with unknown function. Disruption of ire-1 or hac-1 renders N. crassa cells seriously deficient in cellulase secretion. Further investigation of the 39 transcription factors (TFs) that showed differential expression under ER stress uncovered three novel TFs (RES-1, RES-2, RRG-2) that markedly affected cellulase secretion. Conclusions: Here, we determined the transcriptional scope of the ER stress response during lignocellulase synthesis in the model cellulolytic fungus N. crassa. Through genome-wide mutant screening and analysis, dozens of novel genes were discovered to be involved in the process. The findings of this work will be useful for strain improvement to facilitate lignocellulase and biomass-based chemical production.

Project description:Transcription factors play a key role in transcription regulation as they recognize and directly bind to defined sites in promoter regions of target genes, and thus modulate differential expression. The overall process is extremely dynamic, as they have to move through the nucleus and transiently bind to chromatin in order to regulate gene transcription. To identify transcription factors that affect glycogen accumulation in Neurospora crassa, we performed a systematic screen of a deletion strains set generated by the Neurospora Knockout Project and available at the Fungal Genetics Stock Center. In a wild-type strain of N. crassa, glycogen content reaches a maximal level at the end of the exponential growth phase, but upon heat stress the glycogen content rapidly drops. The gene encoding glycogen synthase (gsn) is transcriptionally down-regulated when the mycelium is exposed to the same stress condition. We identified 17 deleted strains having glycogen accumulation profiles different from that of the wild-type strain under both normal growth and heat stress conditions. Most of the transcription factors identified were annotated as hypothetical protein, however some of them, such as the PacC, XlnR, and NIT2 proteins, were biochemically well-characterized either in N. crassa or in other fungi. The identification of some of the transcription factors was coincident with the presence of DNA-binding motifs specific for the transcription factors in the gsn 5'-flanking region, and some of these DNA-binding motifs were demonstrated to be functional by Electrophoretic Mobility Shift Assay (EMSA) experiments. Strains knocked-out in these transcription factors presented impairment in the regulation of gsn expression, suggesting that the transcription factors regulate glycogen accumulation by directly regulating gsn gene expression. Five selected mutant strains showed defects in cell cycle progression, and two transcription factors were light-regulated. The results indicate that there are connections linking different cellular processes, such as metabolism control, biological clock, and cell cycle progression.

Dataset Information

Genome-wide analysis of the endoplasmic reticulum stress response during lignocellulase production in Neurospora crassa.

Publications

Genome-wide analysis of the endoplasmic reticulum stress response during lignocellulase production in Neurospora crassa.

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