A family of covalently linked cell wall proteins of Saccharomyces cerevisiae, called Pir proteins, are characterized by up to 10 conserved repeating units. Ccw5/Pir4p contains only one complete repeating sequence and its deletion caused a release of the protein into the medium. Fungal cell walls are rigid albeit dynamic, complex structures, withstanding intracellular osmotic pressures of more than 10 bar (1). In Saccharomyces cerevisiae the cell wall amounts to about 20% of the total dry weight of the cell. Besides a small amount of chitin, it mainly consists of -glucans and mannoproteins. The actual protein content comes to about 10% of the wall by weight (2). Almost all the proteins are highly Oand N-mannosylated (2-5). Cell wall studies in the past ten to fifteen years have focused on the various cell wall proteins, since the information concerning their function is expected to help understand the biogenesis as well as the dynamic rebuilding and dissolving of this highly intricate, extracellular organelle during budding and mating.By now, more than 30 cell wall proteins have been identified (6 -9). Some of them are solubilized from the cell wall by SDS under reducing conditions and are therefore called soluble cell wall proteins (10), however, most of them are covalently attached to the glucan layer and can be released from SDS-extracted cell walls by -glucanases (11, 12). Two modes of covalent linkage can be distinguished. In the first case the cell wall protein is synthesized as GPI 5 (glycosylphosphatidylinositol) modified intermediate. These are trans-mannosylated by hydrolyzing the oligomannosyl moiety of the GPI lipid anchor and by a subsequent transfer to -1,6-glucan (12-16). This group of covalently attached cell wall proteins, called GPI-Cwp, are released from the wall both by -1,6-and by -1,3-glucanases, due to the attachment of GPI-Cwps to -1,3-glucan via a short -1,6-glucan bridge (4, 12). The second group of covalently linked cell wall proteins are the so-called Pir proteins, named originally according to three genes coding for putative proteins with internal repeats (Pir) (17) and subsequently identified as covalently linked cell wall proteins Ccw1, -2, -3, and -4p (8,18,19). For S. cerevisiae five PIR genes are known (Table 1) coding for proteins with varying numbers of repetitive units (1 to 10). Pir proteins do not contain a C-terminal GPI-addition signal, they are all processed by Kex2 protease, and they are released from intact cells by very mild alkaline treatment (30 mM NaOH, 12 h, 4°C) (8). Pir proteins are attached directly to -1,3-glucan (20) and can therefore be released from S. cerevisiae by the corresponding -1,3-glucanase, not however by -1,6-glucanase (4). The actual alkali labile linkage between the protein moiety and -1,3-glucan is not known. Pir proteins known to be involved in various biological phenomena are not essential for viability; a quadruple mutant, however, possesses a severe growth phenotype (21). Pir2/Ccw7/Hsp150p is strongly induced by heat stress and ni...
In higher plants, sugars are required not only to sustain heterotrophic growth but also to regi a variety of genes. Environmental stresses, such as pathogen infection and wounding, activate a cascade of defense responses and may also affect carbohydrate metabolism. In this study, the relationship between sugar-and stressactivated signal transduction pathways and the underlying regulatoty mechanism was analyzed. Photoautotrophically growing suspension culture cells of Chenopodium rubrum were used as a model system to study the effects of the metabolic regulator o-glucose and of different stress-related stimuli on photosynthesis, sink metabolism, and defense response by analyzing the regulation of mRNAs for representative enzymes of these pathways. Glucose as well as the funga1 elicitor chitosan, the phosphatase inhibitor endothall, and benzoic acid were shown to result in a coordinated regulatoty mechanism. The mRNAs for phenylalanine ammonia-lyase, a key enzyme of defense response, and for the sink-specific extracellular invertase were induced. In contrast, the mRNA for the Calvin cycle enzyme ribulose bisphosphate carboxylase was repressed. This inverse regulatory pattern was also observed in experiments with wounded leaves of C. rubrum plants. The differential effect of the protein kinase inhibitor staurosporine on mRNA regulation demonstrates that the carbohydrate signal and the stress-related stimuli independently activate different intracellular signaling pathways that ultimately are integrated to coordinately regulate source and sink metabolism and activate defense responses. The various stimuli triggered the transient and rapid activation of protein kinases that phosphotylate the myelin basic protein. The involvement of phosphorylation in signal transduction is further supported by the effect of the protein kinase inhibitor staurosporine on mRNA levels.
In higher plants, sugars are required not only to sustain heterotrophic growth but also to regulate the expression of a variety of genes. Environmental stresses, such as pathogen infection and wounding, activate a cascade of defense responses and may also affect carbohydrate metabolism. In this study, the relationship between sugar- and stress-activated signal transduction pathways and the underlying regulatory mechanism was analyzed. Photoautotrophically growing suspension culture cells of Chenopodium rubrum were used as a model system to study the effects of the metabolic regulator D-glucose and of different stress-related stimuli on photosynthesis, sink metabolism, and defense response by analyzing the regulation of mRNAs for representative enzymes of these pathways. Glucose as well as the fungal elicitor chitosan, the phosphatase inhibitor endothall, and benzoic acid were shown to result in a coordinated regulatory mechanism. The mRNAs for phenylalanine ammonia-lyase, a key enzyme of defense response, and for the sink-specific extracellular invertase were induced. In contrast, the mRNA for the Calvin cycle enzyme ribulose bisphosphate carboxylase was repressed. This inverse regulatory pattern was also observed in experiments with wounded leaves of C. rubrum plants. The differential effect of the protein kinase inhibitor staurosporine on mRNA regulation demonstrates that the carbohydrate signal and the stress-related stimuli independently activate different intracellular signaling pathways that ultimately are integrated to coordinately regulate source and sink metabolism and activate defense responses. The various stimuli triggered the transient and rapid activation of protein kinases that phosphorylate the myelin basic protein. The involvement of phosphorylation in signal transduction is further supported by the effect of the protein kinase inhibitor staurosporine on mRNA levels.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.