Mitogen-activated Protein Kinase Pmk1 Research Articles

Specific Functional Features of the Cell Integrity MAP Kinase Pathway in the Dimorphic Fission Yeast Schizosaccharomyces japonicus.

Mitogen activated protein kinase (MAPK) signaling pathways execute essential functions in eukaryotic organisms by transducing extracellular stimuli into adaptive cellular responses. In the fission yeast model Schizosaccharomyces pombe the cell integrity pathway (CIP) and its core effector, MAPK Pmk1, play a key role during regulation of cell integrity, cytokinesis, and ionic homeostasis. Schizosaccharomyces japonicus, another fission yeast species, shows remarkable differences with respect to S. pombe, including a robust yeast to hyphae dimorphism in response to environmental changes. We show that the CIP MAPK module architecture and its upstream regulators, PKC orthologs Pck1 and Pck2, are conserved in both fission yeast species. However, some of S. pombe’s CIP-related functions, such as cytokinetic control and response to glucose availability, are regulated differently in S. japonicus. Moreover, Pck1 and Pck2 antagonistically regulate S. japonicus hyphal differentiation through fine-tuning of Pmk1 activity. Chimeric MAPK-swapping experiments revealed that S. japonicus Pmk1 is fully functional in S. pombe, whereas S. pombe Pmk1 shows a limited ability to execute CIP functions and promote S. japonicus mycelial development. Our findings also suggest that a modified N-lobe domain secondary structure within S. japonicus Pmk1 has a major influence on the CIP signaling features of this evolutionarily diverged fission yeast.

CCK1, a PMK1-type MAP kinase is required for hyphal growth, pigmentation, conidiation, enzyme activity, osmotic stress response, and pathogenicity in Corynespora cassiicola

Corynespora cassiicola is a fungal pathogen causing Corynespora Leaf Fall disease (CLF) in rubber trees (Hevea brasiliensis). CLF has great economic impact in rubber-producing countries. However, the molecular mechanisms involved in the pathogenicity of C. cassiicola remain poorly understood. Mitogen-activated protein kinase (MAPK) is one of the major signaling pathways responsible for regulation of fungal development and virulence in many plant fungal pathogens. The C. cassiicola cck1 gene encodes a MAPK that is homologous to the rice pathogen Magnaporthe grisea MAPK Pmk1 protein. In this study, targeted cck1 gene disruption and complementation experiments were carried out in C. cassiicola. Compared to the wild-type and CΔcck1 complement, the Δcck1 mutant had more pigmentation and exhibited dramatically reduced aerial mycelial mass and mycelial growth rates, along with the inability to produce conidia or conidiophores. In addition, the Δcck1 hyphae were darker in color and had less branches and septae with visibly condensed protoplasm. The Δcck1 mutant was more resistant to hyperosmotic stress, and was able to produce greater amount of laccase and lesser cellulase in vitro; however, the production of laccase was delayed. Importantly, Δcck1 mycelia and crude toxin were less virulent upon inoculation of rubber tree leaves. These findings indicate that the C. cassiicola CCK1 MAP kinase is a versatile regulator involved in nearly every aspect of plant fungal pathogenicity including mycelial growth, development, differentiation, pigmentation, conidiation, production of extracellular degradation enzymes, osmoregulation, and virulence.

Multiple crosstalk between TOR and the cell integrity MAPK signaling pathway in fission yeast.

In eukaryotic cells, the highly conserved Target of Rapamycin (TOR) and the Mitogen Activated Protein Kinase (MAPK) signaling pathways elicit adaptive responses to extra- and intracellular conditions by regulating essential cellular functions. However, the nature of the functional relationships between both pathways is not fully understood. In the fission yeast Schizosaccharomyces pombe the cell integrity MAPK pathway (CIP) regulates morphogenesis, cell wall structure and ionic homeostasis. We show that the Rab GTPase Ryh1, a TORC2 complex activator, cross-activates the CIP and its core member, the MAPK Pmk1, by two distinct mechanisms. The first one involves TORC2 and its downstream effector, Akt ortholog Gad8, which together with TORC1 target Psk1 increase protein levels of the PKC ortholog Pck2 during cell wall stress or glucose starvation. Also, Ryh1 activates Pmk1 in a TORC2-independent fashion by prompting plasma membrane trafficking and stabilization of upstream activators of the MAPK cascade, including PDK ortholog Ksg1 or Rho1 GEF Rgf1. Besides, stress-activated Pmk1 cross-inhibits Ryh1 signaling by decreasing the GTPase activation cycle, and this ensures cell growth during alterations in phosphoinositide metabolism. Our results reveal a highly intricate cross-regulatory relationship between both pathways that warrants adequate cell adaptation and survival in response to environmental changes.

MoRad6-mediated ubiquitination pathways are essential for development and pathogenicity in Magnaporthe oryzae.

The ubiquitin system modulates protein functions through targeting substrates for ubiquitination. Here, E2 conjugating enzyme MoRad6-related ubiquitination pathways are identified and analyzed in Magnaporthe oryzae, the causal agent of rice blast disease. Disruption of MoRad6 leads to severe defects in growth, sporulation, conidial germination, appressorium formation, and plant infection. To depict the functions of MoRad6, three putative ubiquitin ligases, MoRad18, MoBre1 and MoUbr1, are also characterized. Deletion of MoRad18 causes minor phenotypic changes, while MoBre1 is required for growth, conidiation and pathogenicity in M. oryzae. Defects in ΔMobre1 likely resulted from the reduction in di- and tri-methylation level of Histone 3 lysine 4 (H3K4). Notably, MoUbr1 is crucial for conidial adhesion and germination, possibly by degrading components of cAMP/PKA and mitogen-activated protein kinase (MAPK) Pmk1 signaling pathways via the N-end rule pathway. Germination failure of ΔMoubr1 conidia could be rescued by elevation of cAMP level or enhanced Pmk1 phosphorylation resulting from further deletion of MoIra1, the M. oryzae homolog of yeast Ira1/2. These reveal vital effects of cAMP/PKA and MAPK Pmk1 signaling on conidial germination in M. oryzae. Altogether, our results suggest that MoRad6-mediated ubiquitination pathways are essential for the infection-related development and pathogenicity of M. oryzae.

Biological Significance of Nuclear Localization of Mitogen-activated Protein Kinase Pmk1 in Fission Yeast

Mitogen-activated protein kinase (MAPK) signaling pathways play a fundamental role in the response of eukaryotic cells to environmental changes. Also, much evidence shows that the stimulus-dependent nuclear targeting of this class of regulatory kinases is crucial for adequate regulation of distinct cellular events. In the fission yeast Schizosaccharomyces pombe, the cell integrity MAPK pathway, whose central element is the MAPK Pmk1, regulates multiple processes such as cell wall integrity, vacuole fusion, cytokinesis, and ionic homeostasis. In non-stressed cells Pmk1 is constitutively localized in both cytoplasm and nucleus, and its localization pattern appears unaffected by its activation status or in response to stress, thus questioning the biological significance of the presence of this MAPK into the nucleus. We have addressed this issue by characterizing mutants expressing Pmk1 versions excluded from the cell nucleus and anchored to the plasma membrane in different genetic backgrounds. Although nuclear Pmk1 partially regulates cell wall integrity at a transcriptional level, membrane-tethered Pmk1 performs many of the biological functions assigned to wild type MAPK like regulation of chloride homeostasis, vacuole fusion, and cellular separation. However, we found that down-regulation of nuclear Pmk1 by MAPK phosphatases induced by the stress activated protein kinase pathway is important for the fine modulation of extranuclear Pmk1 activity. These results highlight the importance of the control of MAPK activity at subcellular level.