The unfolded protein response (UPR) involves a complex signalling pathway in which the transcription factor HACA plays a central role. Here we report the cloning and characterisation of the hacA gene and its product from Aspergillus niger. ER (endoplasmic reticulum) stress results in the splicing of an unconventional 20-nt intron from the A. niger hacA mRNA, and is associated with truncation of the 5'-end of the hacA mRNA by 230 nt. In this study the UPR was triggered by over expressing tissue plasminogen activator (t-PA), and by treatment of mycelia with dithiothreitol (DTT) or tunicamycin. Overexpression of the processed form of hacA not only led to the up-regulation of bipA, cypB and pdiA--mimicking the UPR--but also led to the up-regulation of the hacA gene itself. In vitro binding assays confirmed that the HACA protein binds to the promoters of genes encoding ER-localised chaperones and foldases, and to the promoter of the hacA gene itself. Finally, a GFP-HACA fusion was shown to localise in the nucleus.

The intercellular washing fluid (IWF) from leaves of sugar beet (Befa vulgaris L.) contains a number of proteins exhibiting in vitro antifungal activity against the devastating leaf pathogen Cercospora beticola (Sacc.). Among these, a potent antifungal peptide, designated IWF4, was identified. The 30-amino-acid residue sequence of IWF4 is rich in cysteines (6) and glycines (7) and has a highly basic isoelectric point. IWF4 shows homology to the chitin-binding (hevein) domain of chitin-binding proteins, e.g. class I and IV chitinases. Accordingly, IWF4 has a strong affinity to chitin. Notably, it binds chitin more strongly than the chitin-binding chitinases. A full-length IWF4 cDNA clone was obtained that codes for a preproprotein of 76 amino acids containing an N-terminal putative signal peptide of 21 residues, followed by the mature IWF4 peptide of 30 residues, and an acidic C-terminal extension of 25 residues. IWF4 mRNA is expressed in the aerial parts of the plant only, with a constitutive expression in young and mature leaves and in young flowers. No induced expression of IWF4 protein or mRNA was detected during infection with C. beficola or after treatment with 2,6-dichloroisonicotinic acid, a well-known inducer of resistance in plants.

Filamentous fungi are important producers of plant polysaccharide degrading enzymes that are used in many industrial applications. These enzymes are produced by the fungus to liberate monomeric sugars that are used as carbon source. Two of the main components of plant polysaccharides are l-arabinose and d-xylose, which are metabolized through the pentose catabolic pathway (PCP) in these fungi. In Aspergillus niger, the regulation of pentose release from polysaccharides and the PCP involves the transcriptional activators AraR and XlnR, which are also present in other Aspergilli such as Aspergillus nidulans. The comparative analysis revealed that the regulation of the PCP by AraR differs in A. nidulans and A. niger, whereas the regulation of the PCP by XlnR was similar in both species. This was demonstrated by the growth differences on l-arabinose between disruptant strains for araR and xlnR in A. nidulans and A. niger. In addition, the expression profiles of genes encoding l-arabinose reductase (larA), l-arabitol dehydrogenase (ladA) and xylitol dehydrogenase (xdhA) differed in these strains. This data suggests evolutionary changes in these two species that affect pentose utilisation. This study also implies that manipulating regulatory systems to improve the production of polysaccharide degrading enzymes, may give different results in different industrial fungi.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-011-3242-2) contains supplementary material, which is available to authorized users.

This study describes two novel regulators, GalX and GalR, that control D-galactose utilization in Aspergillus nidulans. This system is unique for A. nidulans since no GalR homologs were found in other ascomycetes. GalR shares significant sequence identity with the arabinanolytic and xylanolytic regulators AraR and XlnR, but GalX is more distantly related.

A protease-deficient strain of Aspergillus niger has been used as a host for the production of human tissue plasminogen activator (t-PA). In defined medium, up to 0.07 mg t-PA (g biomass)(-1) was produced in batch and fed-batch cultures and production was increased two- to threefold in two-phase batch cultures in which additional glucose was provided as a single pulse at the end of the first batch growth phase. Production was increased [up to 1.9 mg t-PA (g biomass)(-1)] by the addition of soy peptone to the defined medium. The rate of t-PA production in batch cultures supplemented with soy peptone (0.2 to 0.6 mg t-PA L(-1) h(-1)) was comparable to rates observed previously in high-producing mammalian or insect cell cultures. In glucose-limited chemostat culture supplemented with soy peptone, t-PA was produced at a rate of 0.7 mg t-PA L(-1) h(-1). Expression of t-PA in A. niger resulted in increased expression of genes (bipA, pdiA, and cypB) involved in the unfolded protein response (UPR). However, when cypB was overexpressed in a t-PA-producing strain, t-PA production was not increased. The t-PA produced in A. niger was cleaved into two chains of similar molecular weight to two-chain human melanoma t-PA. The two chains appeared to be stable for at least 16 h in culture supernatant of the host strain. However, in general, <1% of the t-PA produced in A. niger was active, and active t-PA disappeared from the culture supernatant during the stationary phase of batch cultures, suggesting that the two-chain t-PA may have been incorrectly processed or that initial proteolytic cleavage occurred within the proteolytic domain of the protein. Total t-PA (detected by enzyme-linked immunoassay) also eventually disappeared from culture supernatants, confirming significant extracellular proteolytic activity, even though the host strain was protease-deficient.

Background: ␣-1,4-Glucan lyase (GLase) is a glycoside hydrolase family member that degrades starch via an elimination reaction. Results: Crystal structures of GLase with covalently bound inhibitors show that the catalytic nucleophile can abstract the proton. Conclusion:The nucleophile has a dual function, acting successively as nucleophile and base. Significance: A single substitution converts a glycoside hydrolase into a lyase.

SummaryEndo-xylanase (from Bacillus subtilis) or ferulic acid esterase (from Aspergillus niger)were expressed in wheat under the control of the endosperm-specific 1DX5 glutenin promoter. Constructs both with and without the endoplasmic reticulum retention signal (Lys-Asp-Glu-Leu) KDEL were used. Transgenic plants were recovered in all four cases but no qualitative differences could be observed whether KDEL was added or not. Endo-xylanase activity in transgenic grains was increased between two and threefold relative to wild type. The grains were shrivelled and had a 25%-33% decrease in mass. Extensive analysis of the cell walls showed a 10%-15% increase in arabinose to xylose ratio, a 50% increase in the proportion of water-extractable arabinoxylan, and a shift in the MW of the water-extractable arabinoxylan from being mainly larger than 85 kD to being between 2 and 85 kD. Ferulic acid esteraseexpressing grains were also shrivelled, and the seed weight was decreased by 20%-50%. No ferulic acid esterase activity could be detected in wild-type grains whereas ferulic acid esterase activity was detected in transgenic lines. The grain cell walls had 15%-40% increase in water-unextractable arabinoxylan and a decrease in monomeric ferulic acid between 13% and 34%. In all the plants, the observed changes are consistent with a plant response that serves to minimize the effect of the heterologously expressed enzymes by increasing arabinoxylan biosynthesis and cross-linking.

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