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Peroxisomal carnitine acetyl transferase is required for elaboration of…
Peroxisomal carnitine acetyl transferase is required for elaboration of pemetration hyphae during plant infection by Magnaporthe grisea
Results
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pth2 (pathogenicity mutants) resulted from inactivation of putative CAT-encoding gene. PTH2 encodes a protein (614 a.a of 69.2 kDa with SKL1 type I peroxisomal targeting sequence at C-terminal -> similar to C. tropicalis CT-CAT2 gene and S. cerevisiae CAT2 gene.
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Appressorial melanin biosynthesis is reduced, but not
severely compromised by absence of PTH2
pth2 mutants might be affected in appressorium function might be due to a requirement for peroxisomal acetyl-CoA as a substrate for dihydroxynaphthalene melanin biosynthesis
Pth2 could generate cytoplasmic acetyl CoA, which is channeled into the pentaketide melanin biosynthesis pathway.
Guy 11 and the melanin-deficient, non-pathogenic mutants alb1 and buf1, which lack polyketide synthase and trihydroxynaphthalene reductase respectively
pth2 mutants, a melanin layer was observed, but was reduced in thickness when compared with Guy 11. Appressorium melanization could,however, be readily observed by phase contrast microscopy in both Guy 11 and Dpth2 mutants
Scytalone is a melanin biosynthetic intermediate, which has previously been shown to restore the ability of alb1 mutants to produce disease lesions
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Experimental procedures
Fungal strains, culture conditions and DNA analysis
wild type and mutant strains of M.grisea stored in lab w standard procedure. growth maintenance, nucleic acid extraction n transformation were performed. gel electropherosis, RE digestion n DNA gel blot hybrid were performed.
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Discussion
Carnitine acetyl transferase- for directing acetyl CoA to the correct intracellular compartment for subsequent utilization
In budding yeast S. cerevisiae, fatty acid B-oxidation occurs only in peroxisome
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Based on result
shown PTH2- encodes the major CAT acitivity in M. grisea based on enzymatic assay and inability of pth2 mutans to utilize acetate or lipids as sole carbon source
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all th enzymes of glyoxylate shut are located in glyoxysomes as suggested for N. crassa - require Pth2 activity for entry of acetyl CoA in this separate compartment
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CAT activity to the plant infection process by M. grisea highlights the dependence of foliar plant pathogen on lipid metabolism - for supporting initial growth and development on leaf surface
Absence of external nutrient- to promote appressorium development by M. grisea means that lipid mobilizatio, peroxisomal fatty acid B-oxidation and generation of a pool of acetyl CoA that allow pathogen to enter its host
anthracnose fungus Colletotrichum lagenarium- which peroxisomal biogenesis shown to be necessary for appressorium function
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Deletion of PEX6 peroxi- encoding prevents peroxisome biogenesis and renders M. girsea completely non-pathogenic that demonstrate the significance of peroxisomal activities in appressorium function
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Woronin bodies- essential for appressorium function in M. girsea highlight the diverse functions fulfilled by peroxisomal compartment in fungi
In whaet pathogen Stagnospora nodorum, brassica pathogen Leptosphaeria maculans and human pathogen Candida albicans
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recent trnascriptional profiling experiment from barley powdery mildew fungus Blumeria graminis - shown coordinated expression of lipid metabolic genes during appressorium mediated plant infection
Pth2- important in defining the spatial regulation and diverse functions of fatty acid B-oxidation during appressorium-mediated plant infection