Two genes encoding a MAP kinase homologue, designated as mpkB and mpkC, were isolated from Aspergillus nidulans by PCR with degenerated primers. The amino acid sequence of MpkB showed 92% - 93% identity to the MAP kinases of diverse phytopathogenic fungi that are involved in differentiation and pathogenicity. The amino acid sequence of MpkC showed 77% - 85% identity to the stress activated protein kinases (SAPKs) of filamentous fungi that play a role in responding to environmental stresses. Deletion of the mpkB gene caused failure in forming the sexual organ cleistothecium in any condition that could induce sexual development, suggesting that MpkB may be essential for transmitting the signals for sexual development. In addition, deletion mutant of mpkB showed a slower hyphal growth and an aberrant conidiophore morphology. Deletion and over-expression mutants of mpkC showed no detectable phenotypes under any conditions provided by various external stresses. Although the mpkB and mpkC genes were constitutively transcribed through entire life span, transcripts of both genes showed varieties in size and abundance according to the developmental stages. The mpkB transcript was hardly detected in the deletion mutant of veA in contrast to highly accumulated in the over-expression mutant of veA. Deletion of mpkB caused a drastic reduction of medA and steA transcript accumulation during sexual reproduction as well as the stuA transcript during both asexual and sexual developments. Taken together these results, we propose that the MpkB MAP kinase has a central role in diverse signaling pathways that mediate sexual development in A. nidulans.
Full conference title:
23rd Fungal Genetics Conference
- Fungal Genetics Conference 23rd (2002)