PLoS ONE (2012) 7 (4 - e36266)

Vijai Bhadauria, Sabine Banniza, Albert Vandenberg, Gopalan Selvaraj and Yangdou Wei (2012)
Peroxisomal alanine: Glyoxylate aminotransferase AGT1 is indispensable for appressorium function of the rice blast pathogen, Magnaporthe oryzae
PLoS ONE 7 (4 - e36266)
Abstract: The role of ß-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 Deltaagt1 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 ß-oxidation of fatty acids to NAD⁺ in peroxisomes. Therefore, it may provide a means to maintain redox homeostasis in appressoria.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Full text of article
Database assignments for author(s): Yangdou Wei, Sabine Banniza

Research topic(s) for pests/diseases/weeds:
molecular biology - genes

---

Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Pyricularia oryzae	Rice (Oryza)