Peroxisomal Alanine : Glyoxylate Aminotransferase AGT1 is indispensable for appressorium function of the rice blast pathogen, Magnaporthe oryzae

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DOIResolve DOI: http://doi.org/10.1371/journal.pone.0036266
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TypeArticle
Journal titlePLoS ONE
ISSN1932-6203
Volume7
Issue4
Pagese36266:1e36266:9; # of pages: 9
SubjectGene Expression Regulation, Fungal; Glyoxylates; Hordeum; Magnaporthe; NAD; Oryza sativa; Oxidation-Reduction; Peroxisomes; Plant Diseases; Protein Transport; Pyruvic Acid; Sequence Deletion; Surface Properties; Transaminases
AbstractThe role of β-oxidation and the glyoxylate cycle in fungal pathogenesis is well documented. However, an ambiguity still remains over their interaction in peroxisomes to facilitate fungal pathogenicity and virulence. In this report, we characterize a gene encoding an alanine, glyoxylate aminotransferase 1 (AGT1) in Magnaporthe oryzae, the causative agent of rice blast disease, and demonstrate that AGT1 is required for pathogenicity of M. oryzae. Targeted deletion of AGT1 resulted in the failure of penetration via appressoria; therefore, mutants lacking the gene were unable to induce blast symptoms on the hosts rice and barley. This penetration failure may be associated with a disruption in lipid mobilization during conidial germination as turgor generation in the appressorium requires mobilization of lipid reserves from the conidium. Analysis of enhanced green fluorescent protein expression using the transcriptional and translational fusion with the AGT1 promoter and open reading frame, respectively, revealed that AGT1 expressed constitutively in all in vitro grown cell types and during in planta colonization, and localized in peroxisomes. Peroxisomal localization was further confirmed by colocalization with red fluorescent protein fused with the peroxisomal targeting signal 1. Surprisingly, conidia produced by the Δagt1 mutant were unable to form appressoria on artificial inductive surfaces, even after prolonged incubation. When supplemented with nicotinamide adenine dinucleotide (NAD+)+pyruvate, appressorium formation was restored on an artificial inductive surface. Taken together, our data indicate that AGT1-dependent pyruvate formation by transferring an amino group of alanine to glyoxylate, an intermediate of the glyoxylate cycle is required for lipid mobilization and utilization. This pyruvate can be converted to non-fermentable carbon sources, which may require reoxidation of NADH generated by the β-oxidation of fatty acids to NAD+ in peroxisomes. Therefore, it may provide a means to maintain redox homeostasis in appressoria.
Publication date
PublisherPLoS ONE
LanguageEnglish
AffiliationNational Research Council Canada; Aquatic and Crop Resource Development
Peer reviewedYes
NRC number55456
NPARC number21268551
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Record identifier9c310e7f-d184-4f9b-9060-a79a4a5235e7
Record created2013-09-25
Record modified2016-05-09
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