Multiple Rice MicroRNAs Are Involved in Immunity against the Blast Fungus Magnaporthe oryzae

Abstract

MicroRNAs (miRNAs) are indispensable regulators for development and defense in eukaryotes. However, the miRNA species have not been explored for rice (Oryza sativa) immunity against the blast fungus Magnaporthe oryzae, the most devastating fungal pathogen in rice production worldwide. Here, by deep sequencing small RNA libraries from susceptible and resistant lines in normal conditions and upon M. oryzae infection, we identified a group of known rice miRNAs that were differentially expressed upon M. oryzae infection. They were further classified into three classes based on their expression patterns in the susceptible japonica line Lijiangxin Tuan Hegu and in the resistant line International Rice Blast Line Pyricularia-Kanto51-m-Tsuyuake that contains a single resistance gene locus, Pyricularia-Kanto 51-m (Pikm), within the Lijiangxin Tuan Hegu background. RNA-blot assay of nine of them confirmed sequencing results. Real-time reverse transcription-polymerase chain reaction assay showed that the expression of some target genes was negatively correlated with the expression of miRNAs. Moreover, transgenic rice plants overexpressing miR160a and miR398b displayed enhanced resistance to M. oryzae, as demonstrated by decreased fungal growth, increased hydrogen peroxide accumulation at the infection site, and up-regulated expression of defense-related genes. Taken together, our data indicate that miRNAs are involved in rice immunity against M. oryzae and that overexpression of miR160a or miR398b can enhance rice resistance to the disease.

Signs of Silence: Small RNAs and Antifungal Responses in Arabidopsis thaliana and Zea mays

“…However, the mechanisms of sRNA-mediated immunity remain largely elusive, especially for host-fungi interactions. In rice cultivars that are susceptible to Magnaporthe oryzae, enhanced resistance could be achieved by overexpressing miR160 and miR398 [37]. MicroRNA160 targets auxin-responsive factor 16 (ARF16), and miR398 regulates superoxide dismutase 2 (SOD2), both known defence-related genes.…”

Identification of Magnaporthe oryzae-elicited rice novel miRNAs and their targets by miRNA and degradome sequencing

“…For example, osa-miR7695 was reported to mediate the negative regulation of natural resistanceassociated macrophage protein 6 (OsNramp6) to rice blast (Campo et al 2013). And, overexpression of miR160a and miR398b enhanced plant resistance by restraining the fungal growth (Li et al 2014). Moreover, it has been verified recently that osa-miR169 negatively regulates rice immunity by differentially repressing its target genes, the NF-YA family members (Li et al 2017).…”

“…MicroRNAs (miRNAs) are one of the most abundant small RNAs (sRNAs) in plants and their typical lengths are 18-25 nucleotides (Li et al 2014). They are a group of endogenous, non-coding sRNAs involved in regulating gene expression mainly via repressing the translation or mediating the cleavage of target mRNA at the post-transcriptional level (Campo et al 2013).…”

Cooperative Regulatory Functions of miR858 and MYB83 during Cyst Nematode Parasitism

“…Once they bind to their target sequences, miRNAs can trigger mRNA degradation or translational repression, causing down-regulation of the target genes. With the fast expansion of high-throughput sequencing platforms, genome-wide identification and differential expression analysis of miRNAs have been accomplished in an increasing number of plant species (Zhang et al, 2011;Li et al, 2014). Despite the large number of miRNA genes showing differential expression under various developmental and stress conditions, only few of these miRNAs have been functionally characterized.…”

“…For example, overexpression of rice miR398b resulted in increasing plant susceptibility to P. syringae via inhibiting callose deposition (Li et al, 2010). In contrast, miR398b overexpression can also enhance plant resistance against the blast fungus Magnaporthe oryzae via increasing the production of hydrogen peroxide (Li et al, 2014). Similarly, it has been shown that miR863-3p can mutually regulate negative and positive mediators of defense signaling in a pathogen infection stage-specific fashion to fine-tune the timing of defense response (Niu et al, 2016).…”