Subtractive hybridizations revealed genes down-regulated in the palA1 mutant strain of Aspergillus nidulans grown at acid pH

FREITAS JS; SILVA EM; LEAL J; GRAS DE; MARTINEZ-ROSSI NM; ROSSI A

Edimburgo

Conferencia; 9th European Conference on Fungal Genetics; 2008

Federation of European Microbiological Societies

The extracellular pH signaling is mediated in A. nidulans by at least seven genes: the six members of the pal activating cascade (pal A, B, C, F, H and I) and pacC, which codes for the transcription factor PacC. The proteolized form of PacC, which occurs by the action of the pal genes at alkaline pH, activates the transcription of alkaline-expressed genes and represses at alkaline pH the transcription of acid-expressed genes. The PalA protein interacts with the YPXL/I motifs in PacC promoting the action of PalB, a calpain-like protease. Thus, whatever the growth pH is, palA1 mutation should cause an acidic-mimicking growth phenotype. This model implies that loss-of-function mutation in any of the six pal genes shall lead to a wild-type acidic growth phenotype regardless of the ambient pH, an effect not observed in the palA1 mutant strain. Employing subtractive hybridizations, we identified genes down-regulated in the palA1 mutant strain of A. nidulans grown in low-Pi medium, at pH 5.0, whose expression should occur only at alkaline pH. Thus, the overexpression of genes at pH 5.0 suggests that palA gene has a function at acid pH and, therefore, the palA1 mutation did not cause an acidic-mimicking growth phenotype.