The HOG1-like MAP kinase Sak1 of Botrytis cinerea is negatively regulated by the upstream histidine kinase Bos1 and is not involved in dicarboximide- and phenylpyrrole-resistance.

In filamentous ascomycetes, HOG-like signal transduction cascades are involved in the resistance to hyper-osmotic conditions and to dicarboximides and phenylpyrroles. The histidine kinase (HK) Bos1 and the mitogen-activated protein kinase (MAPK) Sak1 are important for the adaptation to hyper-osmotic and oxidative stress, development, and pathogenicity in the phytopathogenic fungus Botrytis cinerea. However, bos1Delta and sak1Delta mutants created previously, also presented different phenotypes, especially the sak1Delta mutants were not resistant to high fungicide concentrations. Since both single mutants were constructed in different parental strains, phenotypic variations due to the genetic background might be suspected. In order to establish the relationship between both protein kinases, we analyzed Sak1 phosphorylation under the control of the Bos1 HK and we realized epistasis analysis between bos1Delta and sak1Delta mutations through the construction of isogenic single and double mutants. Our results show that Bos1 negatively regulates Sak1 phosphorylation and that Bos1 regulates certain phenotypes independently of Sak1. They include fungicide susceptibility, adaptation and conidiation on high neutral osmolarity.