The PEX7-Mediated Peroxisomal Import System Is Required for Fungal Development and Pathogenicity in Magnaporthe oryzae

Jaeduk Goh,Kyoung Su Kim,Junhyun Jeon,Yong-Hwan Lee,Jongsun Park,Sook-Young Park,Jae-Hyuk Yu

doi:10.1371/journal.pone.0028220

Abstract

In eukaryotes, microbodies called peroxisomes play important roles in cellular activities during the life cycle. Previous studies indicate that peroxisomal functions are important for plant infection in many phytopathogenic fungi, but detailed relationships between fungal pathogenicity and peroxisomal function still remain unclear. Here we report the importance of peroxisomal protein import through PTS2 (Peroxisomal Targeting Signal 2) in fungal development and pathogenicity of Magnaporthe oryzae. Using an Agrobacterium tumefaciens-mediated transformation library, a pathogenicity-defective mutant was isolated from M. oryzae and identified as a T-DNA insert in the PTS2 receptor gene, MoPEX7. Gene disruption of MoPEX7 abolished peroxisomal localization of a thiolase (MoTHL1) containing PTS2, supporting its role in the peroxisomal protein import machinery. ΔMopex7 showed significantly reduced mycelial growth on media containing short-chain fatty acids as a sole carbon source. ΔMopex7 produced fewer conidiophores and conidia, but conidial germination was normal. Conidia of ΔMopex7 were able to develop appressoria, but failed to cause disease in plant cells, except after wound inoculation. Appressoria formed by ΔMopex7 showed a defect in turgor generation due to a delay in lipid degradation and increased cell wall porosity during maturation. Taken together, our results suggest that the MoPEX7-mediated peroxisomal matrix protein import system is required for fungal development and pathogenicity M. oryzae.

Highlights

Peroxisomes are single-membrane organelles present in most eukaryotes, which compartmentalize a variety of enzymes involved in diverse biochemical processes, necessary for life [1]
TAIL-PCR and inverse PCR showed that ATMT0060C3 contained T-DNA insertion into the second exon region of MGG_01481.6, designated MoPEX7 (Figure S1A)
MoPEX7 encodes a protein with high similarity to Peroxin7 (PEX7) (Figure S2)

Summary

Introduction

Peroxisomes are single-membrane organelles present in most eukaryotes, which compartmentalize a variety of enzymes involved in diverse biochemical processes, necessary for life [1]. Matrix proteins are translocated to peroxisomes by a complex matrix protein import system consisting of several PEXs, while peroxisome membrane proteins are inserted into membranes through PEX3, PEX19 and PEX16 [6]. The process of peroxisomal matrix protein import may be depicted into four steps: (1) binding of receptors to matrix proteins; (2) docking to the peroxisome membrane; (3) translocation into the peroxisome matrix; (4) recycling of the receptors [2]. The PTS cargo– receptor complex enters the peroxisome matrix using the same docking system, but with separate matrix proteins, and is released to the cytosol for recycling of receptors through ubiquitination [2]

Methods

Results

Conclusion