MADS-Box Transcription Factor ZtRlm1 Is Responsible for Virulence and Development of the Fungal Wheat Pathogen Zymoseptoria tritici

Naser Mohammadi,Rahim Mehrabi,Mozaffar Roostaei,Gert H J Kema,Amir Mirzadi Gohari,Ebrahim Mohammadi Goltapeh,Naser Safaie

doi:10.3389/fmicb.2020.01976

Abstract

Zymoseptoria tritici is one of the most economically destructive wheat diseases all over the world and is a model fungal plant pathogen within the ascomycetes. In this study, the instrumental role of the ZtRlm1 gene encoding a MADS-box transcription factor (TF) in the infection process of Z. tritici was functionally characterized as these proteins play critical roles in the global gene regulation required for various developmental and physiological processes. Our infection assays showed that ZtRlm1 mutants were attenuated in disease development as a 30 and 90% reduction in chloro-necrotic lesions and pycnidia formation, respectively, were observed in plants inoculated with ZtRlm1 mutant strains demonstrating that ZtRlm1 is a crucial factor playing a significant role in the late stage of infection corresponding with pycnidial formation. Our expression analysis demonstrated that the transcript level of ZtRlm1 is induced at 2 and 20 days post-inoculation, coinciding with pycnidial sporulation. In addition, microscopic analyses showed that branch intensity and biomass production were significantly reduced, indicating that impaired pycnidia formation is a result of impaired differentiation and biomass production in the ZtRlm1 mutants. Furthermore, melanization, a phenomenon required for fruiting body formation, was significantly hampered in ZtRlm1 mutants as they were not melanized under all tested temperature and media conditions. Overall, our data showed that impaired disease development of the ZtRlm1 mutants is mainly due to the significant impact of ZtRlm1 in different cellular processes, including differentiation, branching, fungal biomass production, and melanization, in which identification of downstream genes are of interest to increase our understanding of this pathosystem.

Highlights

Zymoseptoria tritici (Desm.) Quaedvlieg & Crous (Quaedvlieg et al, 2011), causes septoria tritici blotch (STB), which is one of the most economically destructive wheat diseases all over the worlds
To identify the homolog of Rlm1 in the fully sequenced genome of Z. tritici, a BLASTp search of Z. tritici genome using S. cerevisiae Rlm1 (GenBank number: BAA09658.1) as the query was performed resulting in the retrieval of the homolog of Rlm1 protein
The specific motif, including the 58-amino-acid MADS-box region and 75-aminoacid MEF2 region determining the features of transcription factor (TF) are located at the N terminus region of ZtRlm1

Summary

Introduction

Zymoseptoria tritici (Desm.) Quaedvlieg & Crous (Quaedvlieg et al, 2011) (formerly known as Mycosphaerella graminicola), causes septoria tritici blotch (STB), which is one of the most economically destructive wheat diseases all over the worlds. STB results in imposing remarkable yield losses annually in wheat-growing regions with high rainfall and moderate temperature during. The application of resistant cultivars is the most cost-effective and environmentally friendly approach to manage STB disease (Brown et al, 2015). Only a limited number of resistant cultivars are currently commercially applied to manage this damaging disease (Fraaije et al, 2005; Orton et al, 2011). The importance of STB is increasing, after the introduction of high yielding cultivars that are improved for resistance to other biotic and abiotic stresses.

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