Glycosylation defects activate filamentous growth Kss1 MAPK and inhibit osmoregulatory Hog1 MAPK.

Division of Molecular Cell Signaling, Institute of Medical Sciences, The University of Tokyo, Shirokanedai, Minato-ku, Tokyo, Japan.
The EMBO Journal (Impact Factor: 10.75). 05/2009; 28(10):1380-91. DOI: 10.1038/emboj.2009.104
Source: PubMed

ABSTRACT The yeast filamentous growth (FG) MAP kinase (MAPK) pathway is activated under poor nutritional conditions. We found that the FG-specific Kss1 MAPK is activated by a combination of an O-glycosylation defect caused by disruption of the gene encoding the protein O-mannosyltransferase Pmt4, and an N-glycosylation defect induced by tunicamycin. The O-glycosylated membrane proteins Msb2 and Opy2 are both essential for activating the FG MAPK pathway, but only defective glycosylation of Msb2 activates the FG MAPK pathway. Although the osmoregulatory HOG (high osmolarity glycerol) MAPK pathway and the FG MAPK pathway share almost the entire upstream signalling machinery, osmostress activates only the HOG-specific Hog1 MAPK. Conversely, we now show that glycosylation defects activate only Kss1, while activated Kss1 and the Ptp2 tyrosine phosphatase inhibit Hog1. In the absence of Kss1 or Ptp2, however, glycosylation defects activate Hog1. When Hog1 is activated by glycosylation defects in ptp2 mutant, Kss1 activation is suppressed by Hog1. Thus, the reciprocal inhibitory loop between Kss1 and Hog1 allows only one or the other of these MAPKs to be stably activated under various stress conditions.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Botrytis cinerea is a necrotrophic fungus that infects a wide range of fruit, vegetable and flower crops. Penetration of the host cuticle occurs via infection structures that are formed in response to appropriate plant surface signals. Differentiation of these structures require a highly conserved MAP kinase cascade including the MAP kinase BMP1. In yeast and several plant pathogenic fungi, the signaling mucin Msb2 has been shown to be involved in surface recognition and MAP kinase activation. In this study, a B. cinerea msb2 mutant was generated and characterized. The mutant showed normal growth, sporulation, sclerotia formation and stress resistance. In the absence of nutrients, abnormal germination with multiple germ tubes was observed. In the presence of sugars, normal germination occurred, but msb2 germlings were almost unable to form appressoria or infection cushions on hard surfaces. Nevertheless, the msb2 mutant showed only a moderate delay in lesion formation on different host plants, and it formed expanding lesions like the wild type. Whereas the wild type showed increasing BMP1 phosphorylation during the first hours of germination on hard surfaces, the phosphorylation levels in the msb2 mutant were strongly reduced. Several genes encoding secreted proteins were found to be coregulated by BMP1 and Msb2 during germination. Taken together, B. cinerea Msb2 is likely to represent a hard surface sensor of germlings and hyphae that triggers infection structure formation via activation of the BMP1 MAP kinase pathway. This article is protected by copyright. All rights reserved.
    Molecular Plant Pathology 01/2015; DOI:10.1111/mpp.12234 · 4.49 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Various surface signals are recognized by Magnaporthe oryzae to activate the Pmk1 MAP kinase that is essential for appressorium formation and invasive growth. One of upstream sensors of the Pmk1 pathway is the MoMsb2 signaling mucin. However, the activation of MoMsb2 and its relationship with other sensors is not clear. In this study, we showed that the cleavage and transmembrane domains are essential for MoMsb2 functions. Cleavage of MoMsb2 was further confirmed by western blot analysis and five putative cleavage sites were functionally characterized. Expression of the extracellular region alone partially rescued the defects of Momsb2 in appressorium formation and virulence. The cytoplasmic region of MoMsb2, although dispensable for appressorium formation, was more important for penetration and invasive growth. Interestingly, the Momsb2 cbp1 double mutant deleted of both mucin genes was blocked in Pmk1 activation. It failed to form appressoria on artificial surfaces and was non-pathogenic. In addition, we showed that MoMsb2 interacts with Ras2 but not with MoCdc42 in co-IP assays. Overall, results from this study indicated that the extracellular and cytoplasmic regions of MoMsb2 have distinct functions in appressorium formation, penetration, and invasive growth, and MoMsb2 has overlapping functions with Cbp1 in recognizing environmental signals for Pmk1 activation. This article is protected by copyright. All rights reserved.
    Environmental Microbiology 03/2015; DOI:10.1111/1462-2920.12847 · 6.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Signaling mucins are evolutionarily conserved regulators of signal transduction pathways. The signaling mucin Msb2p regulates the Cdc42p-dependent mitogen activated protein kinase (MAPK) pathway that controls filamentous growth in yeast. Cleavage and release of the glycosylated inhibitory domain of Msb2p is required for MAPK activation. We show here that proteolytic processing of Msb2p was induced by under-glycosylation of its extracellular domain. Cleavage of under-glycosylated Msb2p required the unfolded protein response (UPR), a quality control (QC) pathway that operates in the endoplasmic reticulum (ER). The UPR regulator Ire1p, which detects mis-folded / under-glycosylated proteins in the ER, controlled Msb2p cleavage by regulating transcriptional induction of Yps1p, the major protease that processes Msb2p. Accordingly, the UPR was required for differentiation to the filamentous cell type. Cleavage of Msb2p occurred in conditional trafficking mutants that trap secretory cargo in the endomembrane system. Processed Msb2p was delivered to the PM, and its turnover by the ubiquitin ligase Rsp5p and ESCRT attenuated the filamentous growth pathway. We speculate that QC pathways may broadly regulate signaling glycoproteins and their cognate pathways by recognizing altered glycosylation patterns that can occur in response to extrinsic cues. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Molecular and Cellular Biology 02/2015; 35(8). DOI:10.1128/MCB.01501-14 · 5.04 Impact Factor


Available from