MpkB MAP Kinase is dispendible for production of mycotoxin in Aspergillus nidulans and Aspergillus flavus

Mitogen-activated protein kinase (MAP Kinase) pathways regulates the growth, development and stress responses in most of eukaryotes. Aspergillus nidulans MAP Kinase encoded by mpkB was known to coordinate sexual development as well as secondary metabolism. Also, it had been reported that the mpkB gene could regulate sterigmatocystin (ST) gene expression and produce mycotoxin at low levels. However, the results of the TLC investigation in this study shows that mpkB gene did not affect the ST production and ST related gene expression. In the veA⁺ background, ST production of ΔmpkB, ΔmkkB and ΔmpkBΔmkkB mutants were similar with wild type. Furthermore, whether MpkB constitutively activated or not in the mutants, the result showed no significant effect on the ST production. The biosynthesis genes required for ST production (aflR, stcE and stcU) were constitutively expressed in each mutant of the MAP Kinase module. ST production of mpkB and mkkB mutants was remarkably delayed in the veA1 background as well, suggesting that the ST production is affected by the veA gene but not mpkB. Similarly, in Aspergillus flavus, MpkB ortholog Afl_mpkB mutant couldn’t produce any sclerotia, but it produced aflatoxin B1 normally. So mpkB gene does not affect the expression of genes involved in mycotoxin production such as ST in A. nidulans or aflatoxin B1 in A. flavus. This study suggests that the signal pathway of MpkB MAP Kinase and mycotoxin production were independent.