Osa-miR7695 enhances transcriptional priming in defense responses against the rice blast fungus

Ferran Sánchez-Sanuy,Kazunori Okada,Shiho Tomiyama,Yue-Ie Hsing,Blanca San Segundo,Cristina Peris-Peris,Sonia Campo

doi:10.1186/s12870-019-2156-5

Abstract

BackgroundMicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level in eukaryotes. In rice, MIR7695 expression is regulated by infection with the rice blast fungus Magnaporthe oryzae with subsequent down-regulation of an alternatively spliced transcript of natural resistance-associated macrophage protein 6 (OsNramp6). NRAMP6 functions as an iron transporter in rice.ResultsRice plants grown under high iron supply showed blast resistance, which supports that iron is a factor in controlling blast resistance. During pathogen infection, iron accumulated in the vicinity of M. oryzae appressoria, the sites of pathogen entry, and in cells surrounding infected regions of the rice leaf. Activation-tagged MIR7695 rice plants (MIR7695-Ac) exhibited enhanced iron accumulation and resistance to M. oryzae infection. RNA-seq analysis revealed that blast resistance in MIR7695-Ac plants was associated with strong induction of defense-related genes, including pathogenesis-related and diterpenoid biosynthetic genes. Levels of phytoalexins during pathogen infection were higher in MIR7695-Ac than wild-type plants. Early phytoalexin biosynthetic genes, OsCPS2 and OsCPS4, were also highly upregulated in wild-type rice plants grown under high iron supply.ConclusionsOur data support a positive role of miR7695 in regulating rice immunity that further underpin links between defense and iron signaling in rice. These findings provides a basis to better understand regulatory mechanisms involved in rice immunity in which miR7695 participates which has a great potential for the development of strategies to improve blast resistance in rice.

Highlights

MicroRNAs are small non-coding RNAs that regulate gene expression at the posttranscriptional level in eukaryotes
M. oryzae infection alters Fe distribution in rice leaves In this work, we investigated the cellular distribution of Fe during M. oryzae infection by using the Perls staining
Our results indicate that during M. oryzae infection, genes that function in Fe uptake via strategy I (e.g. OsFRO2) or strategy II (e.g. OsIRO2, OsNAS2) in roots are downregulated in leaves in both wild-type azygous (WT-Az) and MIR7695-Ac plants

Summary

Introduction

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the posttranscriptional level in eukaryotes. Plants have a sophisticated innate immune system for protection against pathogen infection [1, 2]. Pathogen-induced defense responses include the production of reactive oxygen species (ROS), MiRNAs are small noncoding RNAs that modulate gene expression in eukaryotes by triggering sequence-. Numerous miRNAs have been reported to be regulated during pathogen infection, the biological role of most of them remains unknown. These studies have been conducted mainly in the model dicotyledonous plant Arabidopsis thaliana during interaction with the bacterial pathogen Pseudomonas syringae. Further experimental validation is required to better understand the regulatory roles of miRNAs in plant immunity

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