Abstract
Peroxisomes are required for pathogenicity in many phytopathogenic fungi, but the relationships between fungal pathogenicity and peroxisomal function are not fully understood. Here, we report the identification of a T-DNA insertional mutant C445 of Magnaporthe oryzae, which is defective in pathogenicity. Analysis of the mutation confirmed an insertion into the gene MoPEX1, which encodes a putative homologue to peroxin 1. Targeted gene deletion mutants of MoPEX1 were nonpathogenic and were impaired in vegetative growth, conidiation, and appressorium formation. ΔMopex1 mutants formed abnormal, less pigmented, and nonfunctional appressoria, but they were unable to penetrate plant cuticle. The ΔMopex1 mutants were defective in the utilization of fatty acids (e.g., olive oil and Tween-20). Moreover, deletion of MoPEX1 significantly impaired the mobilization and degradation of lipid droplets during appressorium development. Interestingly, deletion of MoPEX1 blocked the import of peroxisomal matrix proteins. Analysis of an M. oryzae strain expressing GFP-MoPEX1 and RFP-PTS1 fusions revealed that MoPex1 localizes to peroxisomes. Yeast two hybrid experiments showed that MoPex1 physically interacts with MoPex6, a peroxisomal matrix protein important for fungal morphogenesis and pathogenicity. Taken together, we conclude that MoPEX1 plays important roles in peroxisomal function and is required for infection-related morphogenesis and pathogenicity in M. oryzae.
Highlights
Peroxisomes contain two types of protein molecules, namely, membrane proteins and matrix proteins, but do not contain DNA or an independent protein synthesis machinery, so the two types of protein are encoded by nuclear genes and synthesized on free polysomes in the cytosol, which are targeted post-translationally to the peroxisomes[16]
M. oryzae can mechanically breach the rice leaf surface using enormous turgor generated in appressoria by accumulating osmolytes such as glycerol[1,2,3]
The degradation of lipids during appressorium formation is an efficient means of rapidly producing glycerol and leads to production of fatty acids for β-oxidation[35], which is the principal means by which fatty acids are degraded
Summary
Peroxisomes contain two types of protein molecules, namely, membrane proteins and matrix proteins, but do not contain DNA or an independent protein synthesis machinery, so the two types of protein are encoded by nuclear genes and synthesized on free polysomes in the cytosol, which are targeted post-translationally to the peroxisomes[16]. PTS1 is a conserved tripeptide (S/A/C) (H/R/K) (I/L/M) at the C-terminus, while PTS2 is a nonapeptide with the consensus motif (R/K) (L/V/I) X5 (H/Q) (L/A), which is located near the N-terminus or at internal locations in proteins[8,20] These signals on matrix proteins are recognized in the cytosol by soluble PTS receptors, Pex[5] for PTS1 proteins and Pex[7] for PTS2 proteins[16,20,21,22]. Proteins involved in peroxisomal biogenesis are named peroxins, which are encoded by PEX genes[23]. In M. oryzae, Pex6-mediated peroxisome biogenesis is essential for appressorium-mediated plant infection[25,26]. Several important genes required for regulating infection and related morphogenesis have been identified via the AtMT library. Our data shows that MoPEX1 is essential for infection-related morphogenesis and pathogenicity in the rice blast fungus
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