The filamentous fungus Aspergillus nidulans senses red using the red light receptor, phytochrome (FphA). In this study, we identified the MAP kinase SakA (also known as HogA) was involved in phytochrome-dependent light sensing by an efficient screening approach. FphA physically interacted with the histidine-containing phosphotransferase (HPt), YpdA in the cytoplasm. Light activation of the SakA pathway depended on FphA. Hence, light plugs into the SakA pathway through phytochrome.