title: GATA-Dependent Glutaminolysis Drives Appressorium Formation in Magnaporthe oryzae by Suppressing TOR Inhibition of cAMP/PKA Signaling.
abstract: Fungal plant pathogens are persistent and global food security threats. To invade their hosts they often form highly specialized infection structures, known as appressoria. The cAMP/ PKA- and MAP kinase-signaling cascades have been functionally delineated as positive-acting pathways required for appressorium development. Negative-acting regulatory pathways that block appressorial development are not known. Here, we present the first detailed evidence that the conserved Target of Rapamycin (TOR) signaling pathway is a powerful inhibitor of appressorium formation by the rice blast fungus Magnaporthe oryzae. We determined TOR signaling was activated in an M. oryzae mutant strain lacking a functional copy of the GATA transcription factor-encoding gene ASD4. Δasd4 mutant strains could not form appressoria and expressed GLN1, a glutamine synthetase-encoding orthologue silenced in wild type. Inappropriate expression of GLN1 increased the intracellular steady-state levels of glutamine in Δasd4 mutant strains during axenic growth when compared to wild type. Deleting GLN1 lowered glutamine levels and promoted appressorium formation by Δasd4 strains. Furthermore, glutamine is an agonist of TOR. Treating Δasd4 mutant strains with the specific TOR kinase inhibitor rapamycin restored appressorium development. Rapamycin was also shown to induce appressorium formation by wild type and Δcpka mutant strains on non-inductive hydrophilic surfaces but had no effect on the MAP kinase mutant Δpmk1. When taken together, we implicate Asd4 in regulating intracellular glutamine levels in order to modulate TOR inhibition of appressorium formation downstream of cPKA. This study thus provides novel insight into the metabolic mechanisms that underpin the highly regulated process of appressorium development.
authors.affiliation: Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
authors.forename: Margarita
authors.initials: M
authors.lastname: Marroquin-Guzman
authors.affiliation: Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Wilson
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology; D018833:Chaperonins / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005656:Fungal Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D056229:Fungal Structures / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D050991:GATA4 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D054884:Host-Pathogen Interactions / Q000187:drug effects; D020082:Magnaporthe / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D009154:Mutation; D009586:Nitrogen Fixation / Q000187:drug effects; D012275:Oryza / Q000382:microbiology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism
chemical_list: D000935:Antifungal Agents; D005656:Fungal Proteins; D050991:GATA4 Transcription Factor; D047428:Protein Kinase Inhibitors; D021122:Protein Subunits; D005973:Glutamine; D000242:Cyclic AMP; D058570:TOR Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D018833:Chaperonins; D005974:Glutamate-Ammonia Ligase; D020123:Sirolimus