Transposable Elements as Stress Adaptive Capacitors Induce Genomic Instability in Fungal Pathogen Magnaporthe oryzae

Sonia Chadha,Mradul Sharma,Kap-Hoon Han

doi:10.1371/journal.pone.0094415

Abstract

A fundamental problem in fungal pathogenesis is to elucidate the evolutionary forces responsible for genomic rearrangements leading to races with fitter genotypes. Understanding the adaptive evolutionary mechanisms requires identification of genomic components and environmental factors reshaping the genome of fungal pathogens to adapt. Herein, Magnaporthe oryzae, a model fungal plant pathogen is used to demonstrate the impact of environmental cues on transposable elements (TE) based genome dynamics. For heat shock and copper stress exposed samples, eight TEs belonging to class I and II family were employed to obtain DNA profiles. Stress induced mutant bands showed a positive correlation with dose/duration of stress and provided evidences of TEs role in stress adaptiveness. Further, we demonstrate that genome dynamics differ for the type/family of TEs upon stress exposition and previous reports of stress induced MAGGY transposition has underestimated the role of TEs in M. oryzae. Here, we identified Pyret, MAGGY, Pot3, MINE, Mg-SINE, Grasshopper and MGLR3 as contributors of high genomic instability in M. oryzae in respective order. Sequencing of mutated bands led to the identification of LTR-retrotransposon sequences within regulatory regions of psuedogenes. DNA transposon Pot3 was identified in the coding regions of chromatin remodelling protein containing tyrosinase copper-binding and PWWP domains. LTR-retrotransposons Pyret and MAGGY are identified as key components responsible for the high genomic instability and perhaps these TEs are utilized by M. oryzae for its acclimatization to adverse environmental conditions. Our results demonstrate how common field stresses change genome dynamics of pathogen and provide perspective to explore the role of TEs in genome adaptability, signalling network and its impact on the virulence of fungal pathogens.

Highlights

Among fungi, filamentous fungal pathogens are the most devastating agents to crops and cause serious animal and human diseases [1]
Stress adaptive capacitance of M. oryzae To determine the prolonged and continuous effects of copper stress on fungal growth and phenotype, M. oryzae cultures were grown on PDA plates in absence or presence of copper (0.1, 1.0, 2.5 and 5.0 mM) for 7 days (Figure 1A)
These findings suggest that M. oryzae cells can resist prolonged exposure to environmentally relevant copper concentrations (Figure 1A)

Summary

Introduction

Filamentous fungal pathogens are the most devastating agents to crops and cause serious animal and human diseases [1] Their enormous genetic diversity poses a challenge to develop durable strategies for pathogen management [2]. Impacts of adaptive changes are evident by tremendous increase in pathogen’s population [1] Adaptive genes such as repetitive DNA are subjected to stronger selective pressure than other genomic regions [5]. Exploring the contribution of TEs in the genome dynamics under environmental cues is imperative to understand fungal adaptation and survival. Genetic variations at these candidate loci might have profound influence on populations, allowing them to persist under changing conditions [8]. Despite its central significance for fungal pathogenicity, one question still poorly understood is how pathogenic fungi alter their genomes for its adaptation under selective pressures

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Conclusion