Abstract
miR169 is a conserved microRNA (miRNA) family involved in plant development and stress-induced responses. However, how miR169 functions in rice immunity remains unclear. Here, we show that miR169 acts as a negative regulator in rice immunity against the blast fungus Magnaporthe oryzae by repressing the expression of nuclear factor Y-A (NF-YA) genes. The accumulation of miR169 was significantly increased in a susceptible accession but slightly fluctuated in a resistant accession upon M. oryzae infection. Consistently, the transgenic lines overexpressing miR169a became hyper-susceptible to different M. oryzae strains associated with reduced expression of defense-related genes and lack of hydrogen peroxide accumulation at the infection site. Consequently, the expression of its target genes, the NF-YA family members, was down-regulated by the overexpression of miR169a at either transcriptional or translational level. On the contrary, overexpression of a target mimicry that acts as a sponge to trap miR169a led to enhanced resistance to M. oryzae. In addition, three of miR169’s target genes were also differentially up-regulated in the resistant accession upon M. oryzae infection. Taken together, our data indicate that miR169 negatively regulates rice immunity against M. oryzae by differentially repressing its target genes and provide the potential to engineer rice blast resistance via a miRNA.
Highlights
Small RNAs are a type of short non-coding RNAs involved in regulation of gene expression either by chromatin methyl modification or by mRNA cleavage or/and translation inhibition (Baulcombe, 2004)
To address the question of how different miR169 isoforms are differentially responsive to M. oryzae infection, we examined the accumulation of the five most abundant miR169 isoforms in the susceptible accession Lijiang xin Tuan Heigu (LTH) and the monogenic resistant accession IRBL9-W that contains the resistance (R) gene Pi-9 (Tsumematsu et al, 2000) and confers high resistance to M. oryzae (Khanna et al, 2015)
Our data confirmed that the abundance of different miR169 isoforms was quite different, with the least abundant being for miR169f/g and miR169n/o, the most abundance being for miR169b/c, and the middle being for miR169a and miR169h/i/j/k/l/m (Figures 1B,C)
Summary
Small RNAs are a type of short non-coding RNAs involved in regulation of gene expression either by chromatin methyl modification or by mRNA cleavage or/and translation inhibition (Baulcombe, 2004). Based on the difference of origin and function, small RNAs are classified into microRNAs (miRNAs) and small interfering RNAs (siRNAs). Both miRNAs and siRNAs are involved in the regulation of diverse biological processes, including growth, development and responses to biotic and abiotic stresses (Katiyar-Agarwal and Jin, 2010; Chen, 2012; Khraiwesh et al, 2012). Increasing evidence indicates that miRNAs are involved in fine-tuning plant immunity against pathogen invasion (Padmanabhan et al, 2009; Katiyar-Agarwal and Jin, 2010).
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