In vitro assays were performed under varying nutritional conditions to investigate the expression of four genes of the fungus Pochonia chlamydosporia, a nematode parasite and a plant growth promoter. The expression levels of a basic leucine zipper (bZIP) transcription factor, a putative phytase, a phospholipase D (PLD) and a monoxygenase of isolate DSM 26985 were, after 8 h incubation in the presence of Meloidogyne incognita eggs, 3, 14, 900 and 67-fold higher than the fungus alone, respectively. M. incognita uninoculated tomato plants alone induced, at 4 h incubation, a phytase transcription sixfold higher than control. Changes in transcript amounts were not significant when the fungus was in the presence of nematode parasitized plants. Further assays performed at different pHs or in the presence of glucose and NH 4 + showed that the bZIP and phytase transcripts reflect early changes in the fungus metabolism. Barley plants treated with P. chlamydosporia isolates IMI 331547 and DSM 26985 showed a pronounced plant growth promotion effect of the former isolate. Phytic acid affected growth of isolates at 1 × 10 −4 ppm concentration, however, the colony diameter increased at 10 ppm. Gene expression data showed that P. chlamydosporia metabolism reflects key biochemical signals proceeding from roots and host nematode eggs.