The septation initiation network (SIN), composed of a conserved SepH (Cdc7p) kinase cascade, plays an essential role in fungal cytokinesis/septation and conidiation for asexual reproduction, while the mitogen-activated protein kinase (MAPK) pathway depends on successive signaling cascade phosphorylation to sense and respond to stress and environmental factors. In this study, a SepH suppressor–PomA in the filamentous fungus A . nidulans is identified as a negative regulator of septation and conidiation such that the pomA mutant is able to cure defects of sepH1 in septation and conidiation and overexpression of pomA remarkably suppresses septation. Under the normal cultural condition, SepH positively regulates the phosphorylation of MAPK-HogA, while PomA reversely affects this process. In the absence of PbsB (MAPKK, a putative upstream member of HogA), PomA and SepH are unable to affect the phosphorylation level of HogA. Under the osmostress condition, the induced phosphorylated HogA is capable of bypassing the requirement of SepH, a key player for early events during cytokinesis but not for MobA/SidB, the last one in the core SIN protein kinase cascade, indicating the osmotic stimuli-induced septation is capable of bypassing requirement of SepH but unable to bypass the whole SIN requirement. Findings demonstrate that crosstalk exists between the SIN and MAPK pathways. PomA and SepH indirectly regulate HogA phosphorylation through affecting HogA-P upstream kinases. Author summary Timely septation and conidiation are essential for fungal asexual reproduction. Here, we identified a putative dual-specificity tyrosine phosphorylation-regulated kinase PomA, as a suppressor of a conserved SepH (Cdc7p) kinase in the septation initiation network (SIN) cascade, is a new identified negative regulator for septation and conidiation in A . nidulans . Our findings indicated that reversible protein phosphorylation of the high-osmolarity glycerol gene hogA regulated by the SIN-SepH-PomA kinase cascade plays a key role for fungal cell septation and asexual reproduction. However, when fungi meet osmostress, they bypass the originally required SIN protein cascade to fit the environmental niches by increasing the phosphorylation of HogA.
【초록키워드】 Crosstalk, Stress, Protein, Phosphorylation, pathway, mutant, fungi, fungal, Signaling, MAPK, regulate, Pathways, protein kinase, mitogen-activated protein kinase, tyrosine, kinases, asexual reproduction, environmental factors, Author, finding, cascade, overexpression, conidiation, nidulans, glycerol, bypass, upstream, cytokinesis, mitogen, septation, suppressor, protein phosphorylation, Affect, Cell, event, conserved, indicated, composed, required, absence, regulated, suppresse, phosphorylated, respond, affecting, environmental niche, asexual, bypassing, nidulan, osmotic, 【제목키워드】 fungal, regulate, affecting, asexual,