Aims:  Chaetomium thermophilum is a soil‐borne thermophilic fungus whose molecular biology is poorly understood. Only a few genes have been cloned from the Chaetomium genus. This study attempted to clone, to sequence and to express a thermostable glucoamylase gene of C. thermophilum. Methods and Results:  First strand cDNA was prepared from total RNA isolated from C. thermophilum and the glucoamylase gene amplified by using PCR. Degenerate primers based on the N‐terminal sequences of the purified glucoamylase according to our previous works and a cDNA fragment encoding the glucoamylase gene was obtained through RT‐PCR. Using RACE‐PCR, full‐length cDNA of glucoamylase gene was cloned from C. thermophilum. The full‐length cDNA of the glucoamylase was 2016 bp and contained a 1797‐bp open reading frame encoding a protein glucoamylase precursor of 599 amino acid residues. The amino‐acid sequence from 31 to 45 corresponded to the N‐terminal sequence of the purified protein. The first 30 amino acids were presumed to be a signal peptide. The alignment results of the putative amino acid sequence showed the catalytic domain of the glucoamylase was high homology with the catalytic domains of the other glucoamylases. The C. thermophilum glucoamylase gene was expressed in Pichia pastoris, and the glucoamylase was secreted into the culture medium by the yeast in a functionally active form. The recombinant glucoamylase purified was a glycoprotein with a size of about 66 kDa, and exhibited optimum catalytic activity at pH 4·5–5·0 and 65°C. The enzyme was stable at 60°C, the enzyme activity kept 80% after 60 min incubation at 70°C. The half‐life was 40 and 10 min under incubation at 80 and 90°C respectively. Conclusions:  A new thermostable glucoamylase gene of C. thermophilum was cloned, sequenced, overexpressed successfully in P. pastoris. Significance and Impact of the Study:  Because of its thermostability and overexpression, this glucoamylase enzyme offers an interesting potential in saccharification steps in both starch enzymatic conversion and in alcohol production.

Insect defensins, are cationic peptides that play an important role in immunity against microbial infection. In the present study, an anionic defensin from Plutella xylostella, (designated as PxDef) was first cloned and characterized. Amino acid sequence analysis showed that the mature peptide owned characteristic six-cysteine motifs with predicted isoelectric point of 5.57, indicating an anionic defensin. Quantitative real-time polymerase chain reaction analysis showed that PxDef was significantly induced in epidermis, fat body, midgut and hemocytes after injection of heat-inactivated Bacillus thuringiensis, while such an induction was delayed by the injection of live B. thuringiensis in the 4th instar larvae of P. xylostella. Knocking down the expression of nuclear transcription factor Dorsal in P. xylostella by RNA interference significantly decreased the mRNA level of PxDef, and increased the sensitivity of P. xylostella larvae to the infection by live B. thuringiensis. The purified recombinant mature peptide (PxDef) showed higher activity against Gram-positive bacteria, with the minimum inhibition concentrations of 1.6 and 2.6 µM against B. thuringiensis and Bacillus subtilis, respectively. To our knowledge, this is the first report about an anionic PxDef, which may play an important role in the immune system of P. xylostella against B. thuringiensis.