Please enable JavaScript.
Coggle requires JavaScript to display documents.
Peroxisomal carnitine acetyl transferase is required for elaboration of…
Peroxisomal carnitine acetyl transferase is required for elaboration of penetration hyphae during plant infection by Magnaporthe grisea
Discussion
Carnitine acetyl transferase is a critical enzyme for directing acetyl CoA to the correct intracellular compartment for subsequent utilization
Cat2 provides a means for peroxisomally generated generated acetyl CoA to be transferred to the cytoplasm, while Cat1 channels acetyl CoA into mitochondria for oxidation via the tricarboxylic acid cycle
-
PTH2 is involved in the supply of acetate units for melanin biosynthesis via the dihydroxynaphthalene pathway
A large body of experimental evidence has shown that appressorium melanization is vital for plant infection by M. grisea
Although there is a reduction in melanization, there is not the primary reason for loss of pathogenicity in ^pth2
-
Although Pth2 activity very likely contributes to melanin biosynthesis, CAT is not essential for turgor generation in appressoria
CAT is therefore of considerably more important to appressorium physiology than simply providing substrate for the glyoxylate cycle.
Perturbation of the pool of cytosolic acetyl CoA, which results from loss of Pth2, is a catastrophic event for the appressorium due to importance of acetyl CoA as a substrate for several metabolic and biosynthetic pathways.
The absence of external nutrients during spore germination, which is essential to promote appressorium development by M. grisea, means that lipid mobilization, peroxisomal fatty acid Beta-oxidation and generation of a pool a acetyl CoA are likely to be vital to allow this fungal pathogen to enter its host
Results
-
7. Appressorial melanin biosynthesis is reduced, but not severely compromised by absence of PTH2
Light and transmission electron microscopy on Dpth2 mutant, Guy 11 and the melanin-deficient, non-pathogenic mutants alb1 and buf1 (lack polyketide synthase and trihydroxynaphthalene reductase)
Guy11 - appressorium cross-sections showed a thin, distinct layer of melanin deposited just outside the plasma membrane of appressoria
Dbuf1 mutant - thick, diffuse layer of microfibrillar melanin precursors present
Dpth2 mutants - melanin layer was observed, but was reduced in thickness than Guy 11
Dpth2 mutants - affected in appressorium function might due to a requirement for peroxisomal acetyl-CoA as a substrate for dihydroxynaphthalene melanin biosynthesis
Appressorium melanization could, however, be readily observed by phase contrast microscopy in both Guy 11 and Dpth2 mutants
-
-
-
-
-
-
-
-
Experimental procedures
Fungal strains, culture conditions and DNA analysis
Standard procedure M. grisea growth, maintenance, nucleic acid extraction and transformation were performed
Standard procedures of gel electrophoresis, restriction enzyme digestion and DNA gel blot hybridization were performed
-
-
-
-
-
-
-
Introduction
- pathogenic microorganisms have to traverse the plant cuticle to gain entry to underlying tissue
- Blast fungus, Magnaporthe grisea causes the most serious disease of cultivated rice and uses an appressorium to break through the tough outer cuticle of a rice leaf
- Initial development of the rice blast fungus occurs on the leaf surface in the absence of external nutrients
Previously, M. grisea spores mobilize lipid bodies to the developing appressorium under control of the Pmk1 MAP kinase pathway and the onset of turgor generation
. Mutants lacking cAMP-dependent protein kinase A are non-pathogenic because they formmisshapen appressoria that do not degrade lipid and are non-functional
Demonstrate that PTH2 encodes the major CAT in M. grisea and is necessary for appressoria to function correctly
Pth2 is regulated by the cyclic AMP response pathway and is located in peroxisomes, which are abundant in appressoria
PTH2 contributes to effective lipid reserve mobilization during appressorium maturation and is necessary for penetration hypha formation and host invasion
Result indicate intracellular transport of peroxisomally generated acetyl-CoA within appresorium is critical to plant infection by rice blast fungus