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Farmer LM, Rinaldi MA, Young PG, Danan CH, Burkhart SE, Bartel B. Disrupting autophagy restores peroxisome function to an Arabidopsis lon2 mutant and reveals a role for the LON2 protease in peroxisomal matrix protein degradation. THE PLANT CELL 2013; 25:4085-100. [PMID: 24179123 PMCID: PMC3877801 DOI: 10.1105/tpc.113.113407] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 09/09/2013] [Accepted: 10/08/2013] [Indexed: 05/18/2023]
Abstract
Peroxisomes house critical metabolic reactions that are essential for seedling development. As seedlings mature, metabolic requirements change, and peroxisomal contents are remodeled. The resident peroxisomal protease LON2 is positioned to degrade obsolete or damaged peroxisomal proteins, but data supporting such a role in plants have remained elusive. Arabidopsis thaliana lon2 mutants display defects in peroxisomal metabolism and matrix protein import but appear to degrade matrix proteins normally. To elucidate LON2 functions, we executed a forward-genetic screen for lon2 suppressors, which revealed multiple mutations in key autophagy genes. Disabling core autophagy-related gene (ATG) products prevents autophagy, a process through which cytosolic constituents, including organelles, can be targeted for vacuolar degradation. We found that atg2, atg3, and atg7 mutations suppressed lon2 defects in auxin metabolism and matrix protein processing and rescued the abnormally large size and small number of lon2 peroxisomes. Moreover, analysis of lon2 atg mutants uncovered an apparent role for LON2 in matrix protein turnover. Our data suggest that LON2 facilitates matrix protein degradation during peroxisome content remodeling, provide evidence for the existence of pexophagy in plants, and indicate that peroxisome destruction via autophagy is enhanced when LON2 is absent.
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Liberti D, Rollins JA, Dobinson KF. Peroxysomal carnitine acetyl transferase influences host colonization capacity in Sclerotinia sclerotiorum. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2013; 26:768-80. [PMID: 23581822 DOI: 10.1094/mpmi-03-13-0075-r] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In lower eukaryotes, the glyoxylate cycle allows cells to utilize two-carbon compounds when simple sugars are not available. In filamentous fungi, glyoxylate metabolism is coupled with β-oxidation of fatty acids, and both are localized to ubiquitous eukaryotic organelles called peroxisomes. Acetyl coenzyme A (acetyl-CoA) produced during β-oxidation is transported via the cytosol into mitochondria for further metabolism. A peroxisomal-specific pathway for acetyl-CoA transport requiring peroxisomal carnitine acetyl transferase (CAT) activity has been identified in Magnaporthe grisea peroxisomes. Here, we report that a Sclerotinia sclerotiorum ortholog of the M. grisea peroxisomal CAT-encoding gene Pth2 (herein designated Ss-pth2) is required for virulence-associated host colonization. Null (ss-pth2) mutants, obtained by in vitro transposon mutagenesis, failed to utilize fatty acids, acetate, or glycerol as sole carbon sources for growth. Gene expression analysis of these mutants showed altered levels of transcript accumulation for glyoxylate cycle enzymes. Ss-pth2 disruption also affected sclerotial, apothecial, and appressorial development and morphology, as well as oxalic acid accumulation when cultured with acetate or oleic acid as sole carbon nutrient sources. Although mutants were able to penetrate and initially colonize host tissue, subsequent colonization was impaired. Genetic complementation with the wild-type Ss-pth2 restored wild-type virulence phenotypes. These findings suggest an essential role in S. sclerotiorum for the peroxisomal metabolic pathways for oxalic acid synthesis and host colonization.
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Affiliation(s)
- D Liberti
- Department of Plant Pathology, University of Florida, Gainesville 32611, USA
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3
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Bartoszewska M, Kiel JAKW. The role of macroautophagy in development of filamentous fungi. Antioxid Redox Signal 2011; 14:2271-87. [PMID: 20712412 DOI: 10.1089/ars.2010.3528] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Autophagy (macroautophagy) is a bulk degradative pathway by which cytoplasmic components are delivered to the vacuole for recycling. This process is conserved from yeast to human, where it is implicated in cancer and neurodegenerative diseases. During the last decade, many ATG genes involved in autophagy have been identified, initially in Saccharomyces cerevisiae. This review summarizes the knowledge on the molecular mechanisms of autophagy using yeast as model system. Although many of the core components involved in autophagy are conserved from yeast to human, there are, nevertheless, significant differences between these organisms, for example, during autophagy initiation. Autophagy also plays an essential role in filamentous fungi especially during differentiation. Remarkably, in these species autophagy may reflect features of both yeast and mammals. This is exemplified by the finding that filamentous fungi lack the S. cerevisiae clade-specific Atg31 protein, but contain Atg101, which is absent in this clade. A reappraisal of genome data further suggests that, similar to yeast and mammals, filamentous fungi probably also contain two distinct phosphatidylinositol 3-kinase complexes. This review also summarizes the state of knowledge on the role of autophagy in filamentous fungi during differentiation, such as pathogenic development, programmed cell death during heteroincompatibility, and spore formation.
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Affiliation(s)
- Magdalena Bartoszewska
- Molecular Cell Biology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands
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4
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Cruz AHDS, Brock M, Zambuzzi-Carvalho PF, Santos-Silva LK, Troian RF, Góes AM, Soares CMDA, Pereira M. Phosphorylation is the major mechanism regulating isocitrate lyase activity in Paracoccidioides brasiliensis yeast cells. FEBS J 2011; 278:2318-32. [PMID: 21535474 DOI: 10.1111/j.1742-4658.2011.08150.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The glyoxylate cycle plays an essential role for anaplerosis of oxaloacetate during growth of microorganisms on carbon sources such as acetate or fatty acids and has been shown to contribute to virulence of several pathogens. Here, we investigated the transcriptional and post-translational regulation of the glyoxylate cycle key enzyme isocitrate lyase (PbICL) in the human pathogenic fungus Paracoccidioides brasiliensis. Although sequence analyses on fungal isocitrate lyases revealed a high phylogenetic conservation, their regulation seems to differ significantly. Closely related Aspergillus species regulate the glyoxylate cycle at the transcriptional level, whereas Pbicl was constitutively expressed in yeast cells. However, only low PbICL activity was detected when cells were grown in the presence of glucose. Two-dimensional gel analyses with subsequent antibody hybridization revealed constitutive production of PbICL, but low PbICL activity on glucose coincided with extensive protein phosphorylation. Since an in vitro dephosphorylation of PbICL from glucose grown cells strongly increased ICL activity and resembled the phosphorylation pattern of highly active acetate grown cells, post-translational modification seems the main mechanism regulating PbICL activity in yeast cells. In agreement, a transfer of yeast cells from glucose to acetate medium increased PbICL activity without requirement of de novo protein synthesis. Thus, inactivation of PbICL by phosphorylation is reversible, denoting a new strategy for the rapid adaptation to changing environmental conditions.
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Affiliation(s)
- Aline H da Silva Cruz
- Laboratório de Biologia Molecular, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, Brazil
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5
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Fleck CB, Schöbel F, Brock M. Nutrient acquisition by pathogenic fungi: nutrient availability, pathway regulation, and differences in substrate utilization. Int J Med Microbiol 2011; 301:400-7. [PMID: 21550848 DOI: 10.1016/j.ijmm.2011.04.007] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
All pathogenic microorganisms have in common that they need to feed on nutrients available from their host. Therefore, the specific interruption of metabolic pathways is a promising approach which could lead to the discovery of new antimicrobial drugs. However, nutrient availability strongly varies in respect to the infected host niche and pathogens may possess different strategies to acquire nutrients. This review focuses on the differences in regulation and use of key metabolic pathways during infection by pathogenic fungi, especially in the filamentous fungus Aspergillus fumigatus and the dimorphic yeast Candida albicans. Besides universal metabolic pathways, emphasis is given on pathways, which are absent in humans and might, therefore, suit as antifungal drug targets. Niche-specific nutrient availability and different physiological strategies complicate the identification of metabolic pathways, which are essential for all pathogens at each step of the infection process.
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Affiliation(s)
- Christian B Fleck
- Leibniz Institute for Natural Product Research and Infection Biology, Hans Knöll Institute, Microbial Biochemistry and Physiology, Beutenbergstr. 11a, 07745 Jena, Germany
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6
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Müller S, Fleck CB, Wilson D, Hummert C, Hube B, Brock M. Gene acquisition, duplication and metabolic specification: the evolution of fungal methylisocitrate lyases. Environ Microbiol 2011; 13:1534-48. [PMID: 21453403 DOI: 10.1111/j.1462-2920.2011.02458.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Gene duplication represents an evolutionary mechanism for expanding metabolic potential. Here we analysed the evolutionary relatedness of isocitrate and methylisocitrate lyases, which are key enzymes of the glyoxylate and methylcitrate cycle respectively. Phylogenetic analyses imply that ancient eukaryotes acquired an isocitrate lyase gene from a prokaryotic source, but it was lost in some eukaryotic lineages. However, protists, oomycetes and most fungi maintained this gene and successfully integrated the corresponding enzyme into the glyoxylate cycle. A second gene, encoding a highly related enzyme, is present in fungi, but absent from other eukaryotes. This methylisocitrate lyase is specifically involved in propionyl-CoA degradation via the methylcitrate cycle. Although bacteria possess methylisocitrate lyases with a structural fold similar to that of isocitrate lyases, their sequence identity to fungal methylisocitrate lyases is low. Phylogenetic analyses imply that fungal methylisocitrate lyases arose from gene duplication of an ancient isocitrate lyase gene from the basidiomycete lineage. Mutagenesis of active-site residues of a bacterial and fungal isocitrate lyase, which have been predicted to direct the substrate specificity of iso- and methylisocitrate lyases, experimentally confirmed the possibility of direct evolution of methylisocitrate lyases from isocitrate lyases. Thus, gene duplication has increased the metabolic capacity of fungi.
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Affiliation(s)
- Sebastian Müller
- Leibniz Institute for Natural Product Research and Infection Biology e.V., -Hans Knoell Institute-, Jena, Germany
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7
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Lee SH, Han YK, Yun SH, Lee YW. Roles of the glyoxylate and methylcitrate cycles in sexual development and virulence in the cereal pathogen Gibberella zeae. EUKARYOTIC CELL 2009; 8:1155-64. [PMID: 19525419 PMCID: PMC2725564 DOI: 10.1128/ec.00335-08] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2008] [Accepted: 06/01/2009] [Indexed: 11/20/2022]
Abstract
The glyoxylate and methylcitrate cycles are involved in the metabolism of two- or three-carbon compounds in fungi. To elucidate the role(s) of these pathways in Gibberella zeae, which causes head blight in cereal crops, we focused on the functions of G. zeae orthologs (GzICL1 and GzMCL1) of the genes that encode isocitrate lyase (ICL) and methylisocitrate lyase (MCL), respectively, key enzymes in each cycle. The deletion of GzICL1 (DeltaGzICL1) caused defects in growth on acetate and in perithecium (sexual fruiting body) formation but not in virulence on barley and wheat, indicating that GzICL1 acts as the ICL of the glyoxylate cycle and is essential for self-fertility in G. zeae. In contrast, the DeltaGzMCL1 strains failed to grow on propionate but exhibited no major changes in other traits, suggesting that GzMCL1 is required for the methylcitrate cycle in G. zeae. Interestingly, double deletion of both GzICL1 and GzMCL1 caused significantly reduced virulence on host plants, indicating that both GzICL1 and GzMCL1 have redundant functions for plant infection in G. zeae. Thus, both GzICL1 and GzMCL1 may play important roles in determining major mycological and pathological traits of G. zeae by participating in different metabolic pathways for the use of fatty acids.
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Affiliation(s)
- Seung-Ho Lee
- Department of Agricultural Biotechnology, Centers for Fungal Pathogenesis and Agricultural Biomaterials, Seoul National University, South Korea
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8
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Mysyakina IS, Funtikova NS. Activity of NAD-dependent isocitrate dehydrogenase, isocitrate lyase, and malate dehydrogenase in Mucor circinelloides var. lusitanicus INMI under different modes of nitrogen supply. Microbiology (Reading) 2008. [DOI: 10.1134/s0026261708040036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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9
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Mysyakina IS, Funtikova NS. Metabolic characteristics and lipid composition of yeastlike cells and mycelium of Mucor circinelloides var. lusitanicus INMI grown at a high glucose content in the medium. Microbiology (Reading) 2008. [DOI: 10.1134/s0026261708040048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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10
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Abba' S, Balestrini R, Benedetto A, Rottensteiner H, De Lucas JR, Bonfante P. The role of the glyoxylate cycle in the symbiotic fungus Tuber borchii: expression analysis and subcellular localization. Curr Genet 2007; 52:159-70. [PMID: 17701038 DOI: 10.1007/s00294-007-0149-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 07/09/2007] [Accepted: 07/20/2007] [Indexed: 11/26/2022]
Abstract
Expression profiles of isocitrate lyase (TbICL), malate synthase (TbMLS) and fructose-1,6-bisphosphatase (TbFBP) from the mycorrhizal ascomycete Tuber borchii were investigated by real-time RT-PCR in fruiting bodies at different stages of maturation. In addition, a time course experiment was set up to determine how the transcription profile of TbICL, TbMLS and TbFBP in axenic-grown mycelia is affected by different carbon sources. The transcript levels of the three genes in the fruiting bodies were all much higher than those measured in the vegetative stage. The investigation on axenic-grown mycelia revealed that the main positive regulator of TbICL and TbMLS gene expression is the availability of acetate and ethanol, while oleic acid is a too complex substrate for the limited degradative capacities of T. borchii. Immunolabelling on axenic-grown mycelia showed a co-localization of TbICL and the peroxisomal marker protein FOX2. This result demonstrated that in T. borchii ICL is compartmentalized in peroxisomes. The high induction of TbICL, TbMLS and TbFBP transcription and the translocation of lipids in fruiting bodies let us hypothesize that glyoxylate cycle and gluconeogenesis are key metabolic pathways in the recycling of existing cell material and the channelling towards the biosynthesis of new cell components during the maturation of fruiting bodies.
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Affiliation(s)
- Simona Abba'
- Dipartimento di Biologia Vegetale, Università di Torino and Istituto per la Protezione delle Piante del CNR-Sezione di Torino, Viale Mattioli 25, 10125 Turin, Italy.
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11
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Idnurm A, Giles SS, Perfect JR, Heitman J. Peroxisome function regulates growth on glucose in the basidiomycete fungus Cryptococcus neoformans. EUKARYOTIC CELL 2006; 6:60-72. [PMID: 17041184 PMCID: PMC1800366 DOI: 10.1128/ec.00214-06] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The function of the peroxisomes was examined in the pathogenic basidiomycete Cryptococcus neoformans. Recent studies reveal the glyoxylate pathway is required for virulence of diverse microbial pathogens of plants and animals. One exception is C. neoformans, in which isocitrate lyase (encoded by ICL1) was previously shown not to be required for virulence, and here this was extended to exclude also a role for malate synthase (encoded by MLS1). The role of peroxisomes, in which the glyoxylate pathway enzymes are localized in many organisms, was examined by mutation of two genes (PEX1 and PEX6) encoding AAA (ATPases associated with various cellular activities)-type proteins required for peroxisome formation. The pex1 and pex6 deletion mutants were unable to localize the fluorescent DsRED-SKL protein to peroxisomal punctate structures, in contrast to wild-type cells. pex1 and pex6 single mutants and a pex1 pex6 double mutant exhibit identical phenotypes, including abolished growth on fatty acids but no growth difference on acetate. Because both icl1 and mls1 mutants are unable to grow on acetate as the sole carbon source, these findings demonstrate that the glyoxylate pathway can function efficiently outside the peroxisome in C. neoformans. The pex1 mutant exhibits wild-type virulence in a murine inhalation model and in an insect host, demonstrating that peroxisomes are not required for virulence under these conditions. An unusual phenotype of the pex1 and pex6 mutants was that they grew poorly with glucose as the carbon source, but nearly wild type with galactose, which suggested impaired hexokinase function and that C. neoformans peroxisomes might function analogously to the glycosomes of the trypanosomid parasites. Deletion of the hexokinase HXK2 gene reduced growth in the presence of glucose and suppressed the growth defect of the pex1 mutant on glucose. The hexokinase 2 protein of C. neoformans contains a predicted peroxisome targeting signal (type 2) motif; however, Hxk2 fused to fluorescent proteins was not localized to peroxisomes. Thus, we hypothesize that glucose or glycolytic metabolites are utilized in the peroxisome by an as yet unidentified enzyme or regulate a pathway required by the fungus in the absence of peroxisomes.
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Affiliation(s)
- Alexander Idnurm
- Room 322 CARL Building, Box 3546, Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA
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Sakai S, Nishide T, Munir E, Baba K, Inui H, Nakano Y, Hattori T, Shimada M. Subcellular localization of glyoxylate cycle key enzymes involved in oxalate biosynthesis of wood-destroying basidiomycete Fomitopsis palustris grown on glucose. Microbiology (Reading) 2006; 152:1857-1866. [PMID: 16735748 DOI: 10.1099/mic.0.28702-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
This study investigated the subcellular localization of key enzymes of the glyoxylate cycle, i.e. isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (EC 2.3.3.9), that function constitutively in coordination with oxalate biosynthesis of glucose-grownFomitopsis palustris. The ICL purified previously fromF. palustrisis termed FPICL1. Subcellular fractionation analysis of the cell homogenate by the sucrose density-gradient method showed that both key enzymes were present in peroxisomes, whereas acetyl-CoA synthase (EC 6.2.1.1) and oxalate-producing oxaloacetate acetylhydrolase (EC 3.7.1.1) were cytosolic. The peroxisomal localization of FPICL1 was further confirmed by electron microscopic and immunocytochemical analysis with anti-FPICL1 antibody. In addition, the peroxisomal target signal, composed of SKL at the C terminus of the cDNA encoding FPICL1, was found, which also suggests that FPICL1 is peroxisomal. Accordingly, it is postulated that transportation of succinate from peroxisomes to mitochondria, and vice versa, for the transportation of isocitrate or citrate, occurs in glucose-grownF. palustrisfor the constitutive metabolic coordination of the TCA and glyoxylate cycles with oxalate biosynthesis.
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Affiliation(s)
- Shunsuke Sakai
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Tatsunori Nishide
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Erman Munir
- University of North Sumatra, Jl. Bioteknologi No. 1 Kampus USU, Medan 20513, Indonesia
| | - Kei'ichi Baba
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Hiroshi Inui
- Department of Applied Biological Chemistry, University of Osaka Prefecture, Sakai, Osaka 599-8231, Japan
| | - Yoshihisa Nakano
- Department of Applied Biological Chemistry, University of Osaka Prefecture, Sakai, Osaka 599-8231, Japan
| | - Takefumi Hattori
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Mikio Shimada
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
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Flores CL, Gancedo C. Yarrowia lipolytica mutants devoid of pyruvate carboxylase activity show an unusual growth phenotype. EUKARYOTIC CELL 2005; 4:356-64. [PMID: 15701798 PMCID: PMC549329 DOI: 10.1128/ec.4.2.356-364.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2004] [Accepted: 12/02/2004] [Indexed: 11/20/2022]
Abstract
We have cloned and characterized the gene PYC1, encoding the unique pyruvate carboxylase in the dimorphic yeast Yarrowia lipolytica. The protein putatively encoded by the cDNA has a length of 1,192 amino acids and shows around 70% identity with pyruvate carboxylases from other organisms. The corresponding genomic DNA possesses an intron of 269 bp located 133 bp downstream of the starting ATG. In the branch motif of the intron, the sequence CCCTAAC, not previously found at this place in spliceosomal introns of Y. lipolytica, was uncovered. Disruption of the PYC1 gene from Y. lipolytica did not abolish growth in glucose-ammonium medium, as is the case in other eukaryotic microorganisms. This unusual growth phenotype was due to an incomplete glucose repression of the function of the glyoxylate cycle, as shown by the lack of growth in that medium of double pyc1 icl1 mutants lacking both pyruvate carboxylase and isocitrate lyase activity. These mutants grew when glutamate, aspartate, or Casamino Acids were added to the glucose-ammonium medium. The cDNA from the Y. lipolytica PYC1 gene complemented the growth defect of a Saccharomyces cerevisiae pyc1 pyc2 mutant, but introduction of either the S. cerevisiae PYC1 or PYC2 gene into Y. lipolytica did not result in detectable pyruvate carboxylase activity or in growth on glucose-ammonium of a Y. lipolytica pyc1 icl1 double mutant.
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Affiliation(s)
- Carmen-Lisset Flores
- Instituto de Investigaciones Biomédicas Alberto Sols, CSIC-Universidad Autónoma de Madrid, Madrid, Spain.
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14
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Abstract
Beta-oxidation (beta-ox) occurs exclusively in the peroxisomes of Saccharomyces cerevisiae and other yeasts, leading to the supposition that fungi lack mitochondrial beta-ox. Here we present unequivocal evidence that the filamentous fungus Aspergillus nidulans houses both peroxisomal and mitochondrial beta-ox. While growth of a peroxisomal beta-ox disruption mutant (DeltafoxA) was eliminated on a very long-chain fatty acid (C(22:1)), growth was only partially impeded on a long-chain fatty acid (C(18:1)) and was not affected at all on short chain (C4-C6) fatty acids. In contrast, growth of a putative enoyl-CoA hydratase mutant (DeltaechA) was abolished on short-chain and severely restricted on long- and very long-chain fatty acids. Furthermore fatty acids inhibited growth of the DeltaechA mutant but not the DeltafoxA mutant in the presence of an alternate carbon source (lactose). Disruption of echA led to a 28-fold reduction in 2-butenoyl-CoA hydratase activity in a preparation of organelles. EchA was also required for growth on isoleucine and valine. The subcellular localization of the FoxA and EchA proteins was confirmed through the use of red and green fluorescent protein fusions.
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Affiliation(s)
- Lori A Maggio-Hall
- Department of Plant Pathology, University of Wisconsin-Madison, 882 Russell Labs, 1630 Linden Drive, Madison, WI 53706, USA
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15
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Abstract
Peroxisomes are essential organelles in many eukaryotes. Until recently, the main focus of the investigations concerning these important organelles was to understand the biogenesis of the peroxisome (induction, proliferation and matrix protein import). However, when peroxisomes become redundant they are quickly degraded by highly selective processes known as pexophagy. The first molecular studies on pexophagy have indicated that this process shares many features with certain transport pathways to the vacuole (vacuolar protein sorting, autophagy, cytoplasm-to-vacuole targeting and endocytosis). Nevertheless, recent data demonstrate that in addition to common genes also unique genes are required for these transport processes. The main focus for the future should therefore be on identifying the unique determinants of pexophagy. Earlier results suggest that in the methylotrophic yeast Hansenula polymorpha proteins located on the peroxisome itself are required for pexophagy. Thus, it has become essential to study in detail the role of peroxisomal membrane proteins in the degradation process. This review highlights the main achievements of the last few years, with emphasis on H. polymorpha.
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Affiliation(s)
- Adriana N Leão
- Eukaryotic Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Kerklaan 30, 9751 NN, Haren, The Netherlands
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16
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Schadeck RJG, Randi MAF, de Freitas Buchi D, Leite B. Vacuolar system of ungerminated Colletotrichum graminicola conidia: convergence of autophagic and endocytic pathways. FEMS Microbiol Lett 2003; 218:277-83. [PMID: 12586404 DOI: 10.1111/j.1574-6968.2003.tb11529.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Vacuoles of ungerminated Colletotrichum graminicola conidia engulf cytoplasmic structures by a process analogous to microautophagy, demonstrated by using a vacuolar membrane acid phosphatase marker. Fusion of vesicles with vacuoles, without deposition of the acid phosphatase reaction product has been observed, suggesting other pathways of material delivery to vacuoles than microautophagy. Plasma membrane invaginations, multivesicular bodies and retention of neutral red into small vesicles, which were internalized by the vacuole, were verified. These results provided evidence for endocytosis and an active endosomal system. Together, our findings with C. graminicola demonstrated that vacuoles are very dynamic compartments, playing roles in autophagy and endocytic processes.
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Affiliation(s)
- Ruth Janice Guse Schadeck
- Department of Cellular Biology, Federal University of Paraná, C.P. 19031, 81531-990, PR, Curitiba, Brazil
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17
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Affiliation(s)
- Fulvio Reggiori
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109-1048, USA
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Lammers PJ, Jun J, Abubaker J, Arreola R, Gopalan A, Bago B, Hernandez-Sebastia C, Allen JW, Douds DD, Pfeffer PE, Shachar-Hill Y. The glyoxylate cycle in an arbuscular mycorrhizal fungus. Carbon flux and gene expression. PLANT PHYSIOLOGY 2001. [PMID: 11706207 DOI: 10.1104/pp.010375] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Lipid, which is the dominant form of stored carbon in the fungal partner and which fuels spore germination, is made by the fungus within the root and is exported to the extraradical mycelium. We tested the hypothesis that the glyoxylate cycle is central to the flow of carbon in the AM symbiosis. The results of (13)C labeling of germinating spores and extraradical mycelium with (13)C(2)-acetate and (13)C(2)-glycerol and analysis by nuclear magnetic resonance spectroscopy indicate that there are very substantial fluxes through the glyoxylate cycle in the fungal partner. Full-length sequences obtained by polymerase chain reaction from a cDNA library from germinating spores of the AM fungus Glomus intraradices showed strong homology to gene sequences for isocitrate lyase and malate synthase from plants and other fungal species. Quantitative real-time polymerase chain reaction measurements show that these genes are expressed at significant levels during the symbiosis. Glyoxysome-like bodies were observed by electron microscopy in fungal structures where the glyoxylate cycle is expected to be active, which is consistent with the presence in both enzyme sequences of motifs associated with glyoxysomal targeting. We also identified among several hundred expressed sequence tags several enzymes of primary metabolism whose expression during spore germination is consistent with previous labeling studies and with fluxes into and out of the glyoxylate cycle.
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Affiliation(s)
- P J Lammers
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88001, USA
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