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

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.

Systemic induction of phosphatidylinositol-based signaling in leaves of arbuscular mycorrhizal rice plants

“…Rice seedlings were bottom-watered during the whole experiment. Fertirrigation was supplied at nine days after F. mosseae inoculation, using a modified Hoagland half-strength solution (15 ml, every two days) containing 2.5 mM KNO 3 , 2.5 mM Ca(NO 3 ) 2 ·4H 2 O, 1 mM MgSO 4 ·7H 2 O, 0.5 mM NH 4 NO 3 , 25 μM KH 2 PO 4 , 23.15 μM H 3 BO 3 , 4.55 μM MnCl 2 ·4H 2 O, 0.38 μM ZnSO 4 ·7H 2 O, 0.1 μM CuSO 4 ·5H 2 O, 0.14 μM Na 2 MoO 4 ·2H 2 O, 26 μM Fe-EDDHA, pH 5.5) 65 .…”

“…An average of 32 736 498 clean reads/library were reported (Supplementary Table S6). Raw 125 bp paired-end reads processing and analysis were carried out as previously described 65 . RNA-Seq raw data are available at the NCBI GEO database (https ://www.ncbi.nlm.nih.gov/geo) under the accession number GSE148574.…”

“…At 23 days after AMF inoculation, the youngest totally expanded leaves were harvested. Chlorophyll content of rice leaves was determined using a chlorophyll meter (SPAD 502 Plus Chlorophyll Meter, Spectrum Technologies) as previously described 65 . Pi content of rice leaves was determined using a colorimetric as previously described 70 .…”

Contribution of Small RNA Pathway to Interactions of Rice with Pathogens and Insect Pests

“…More than 70 miRNAs respond to M. oryzae or its elicitors (Li et al 2019c). Among these miRNAs, five have been identified as positive regulators in rice blast resistance, namely miR160a, miR162a, miR166k-h, miR398b, and miR7695, whereas eight have been identified as negative regulators, namely miR156, miR164a, miR167d, miR169a, miR319b, miR396, miR1873, and miR444b.2 (Chandran et al 2018;Li et al 2020a;Li et al 2019b;Li et al 2014;Li et al 2017;Salvador-Guirao et al 2018;Sanchez-Sanuy et al 2019;Wang et al 2018b;Xiao et al 2017;Zhang et al 2018b;Zhang et al 2020;Zhao et al 2020;Zhou et al 2020). Obviously, many miRNAs play a role in regulating rice-M. oryzae interactions.…”

“…Overexpression of miR7695 results in increased iron accumulation, enhanced innate immune responses, and increased accumulation of phytoalexins. Further studies revealed that high concentration of iron improves the expression of OsCPS2 and OsCPS4, which function in the first cyclization steps of phytoalexin biosynthesis, suggesting that miR7695 may promote phytoalexins accumulation via controlling the transport of iron (Campo et al 2013;Sanchez-Sanuy et al 2019;Toyomasu et al 2015). Second, miR398b is a well-elucidated positive regulator in rice resistance against M. oryzae.…”