A time course analysis of the extracellular proteome and transcriptome of Aspergillus nidulans growing on sorghum stover

Full title: 

A time course analysis of the extracellular proteome and transcriptome of Aspergillus nidulans growing on sorghum stover

Author: 

Saykhedkar, Sayali Subhash

Year: 

2012

Reference type: 

Thesis

ISBN/ISSN: 

9781267590886

Abstract: 

Scope and method of study: To study the plant cell wall degradation process and changes in overall physiology during the growth of A. nidulans on sorghum stover at proteomic and genomic level, A. nidulans was grown on sorghum stover under solid-state culture conditions for 1, 2, 3, 5, 7 and 14 days. Semi-quantitative extracellular proteome analysis (1-D PAGE LC-MS/MS), whole genome microarray analysis, scanning and transmission electron microscopy, along with qualitative and quantitative analysis of extracellular hydrolytic enzyme activities, and analysis of the breakdown products by enzymes was used to study sorghum cell wall degradation by A. nidulans.Findings and conclusions: Based on analysis of chitin content, A. nidulans grew to be 4-5% of the total biomass in the culture. A hyphal mat developed on the surface of the sorghum by day one and as seen by scanning electron microscopy the hyphae enmeshed the sorghum particles by day 5. A total of 294 extracellular proteins were identified with hemicellulases, cellulases, polygalacturonases, chitinases, esterases and lipases predominating the secretome. Time course analysis revealed a total of 196, 166, 172 and 182 proteins on day 1, 3, 7 and 14 respectively. The fungus used 20% of the xylan and cellulose by day 7 and 30% by day 14. Cellobiose dehydrogenase, feruloyl esterases, and CAZy family 61 endoglucanases, all of which are thought to reduce the recalcitrance of biomass to hydrolysis, were found in high abundance. Total 137 out of 201 transcripts encoding different classes of carbohydrate active enzymes (CAZy) showed significant changes in gene expression throughout the entire time course. Notably upregulated genes in transcriptome analysis included those encoding for hydrolytic enzymes for plant cell wall degradation, protein and lipid degradation, transportation of sugars and amino acids, secondary metabolism fungal cell wall growth, degradation remodeling, glyoxylate pathway and genes encoding proteins of unknown function. Proteome and transcriptome analysis show that A. nidulans secretes a wide array of enzymes to degrade the major polysaccharides and lipids (but probably not lignin) by 1 day of growth on sorghum. The data suggests simultaneous breakdown of hemicellulose, cellulose and pectin. Despite secretion of most of the enzymes on day 1, changes in the relative abundances of enzymes over the time course indicates that the set of enzymes secreted is tailored to the specific substrates available. Our findings reveal that A. nidulans is capable of degrading the major polysaccharides in sorghum without any chemical pre-treatment.