The MpkB MAP kinase plays a role in autolysis and conidiation of Aspergillus nidulans

The mpkB gene of Aspergillus nidulans encodes a MAP kinase homologous to Fus3p of Saccharomyces cerevisiae which is involved in conjugation process. MpkB is required for completing the sexual development at the anastomosis and post-karyogamy stages. The mpkB deletion strain could produce conidia under the repression condition of conidiation such as sealing and even in the submerged culture concomitant with persistent brlA expression, implying that MpkB might have a role in timely regulation of brlA expression. The submerged culture of the deletion strain showed typical autolytic phenotypes including decrease in dry cell mass (DCM), disorganization of mycelial balls, and fragmentation of hyphae. The chiB, engA and pepJ genes which are encoding cell wall hydrolytic enzymes were transcribed highly in the submerged culture. Also, we observed that the enzyme activity of chitinase and glucanase in the submerged culture of mpkB deletion strain was much higher than that of wild type. The deletion of mpkB also caused a precocious germination of conidia and reduction of spore viability. The expression of the vosA gene, a member of velvet gene family, was not observed in the mpkB deletion strain. These results suggest that MpkB should have multiple roles in germination and viability of conidia, conidiation and autolysis through regulating the expression of vosA and brlA.