MiRNA and phasiRNAs-mediated regulation of TIR-NBS-LRR defense genes inArabidopsis thaliana

Abstract

Plants encode large numbers of intracellular immune receptors known as resistance (R) proteins or nucleotide-binding (NB) leucine-rich repeat (LRR) receptors (NLRs), involved in perception of pathogen-derived effectors and activation of immunity.Here, we report a two-tiered regulatory network mediated by microRNA and secondary phased small RNAs (phasiRNA) that targets the silencing of dozens of NLR genes encoding yet uncharacterized members of the Toll/interleukin-1 (TIR)-NBS-LRR (TNLs) subfamily in Arabidopsis. We show that miR825-5p downregulates expression of Arabidopsis AT5G38850 gene (renamed as microRNA-silenced TNL 1 or MIST1) by targeting the sequence coding for a highly conserved functional amino acid motif (TIR2) within the TIR domain of the receptor. Further, we show that MIST1 functions as a regulatory hub, since miRNA825-5p triggers RDR6-mediated processing of MIST1 transcripts, to generate trans-acting phasiRNAs that in turn target, a wide network of TNL genes for gene silencing. Regulation through MIST1 affects disease resistance against the model bacterial pathogen Pseudomonas syringae, since altered levels of miRNA825-5p lead to changes in Arabidopsis ability to establish basal defenses against this pathogen. MiR825-5p is expressed in unchallenged adult leaves and its production is down regulated in response to PAMPs such as bacterial flagellin but also fungal chitin.

Molecular features of RNA silencing against phloem-restricted polerovirus TuYV enable amplification of silencing signal from host transcripts

“…This showed a similar kinetic to that of VIGS, with only 43,3% of the ago1-57 plants exhibiting infection, while infection of ago1-57 with TuMV-GFP and TRV-PDS reached 100% ( Figure S3A ). We hypothesized that this observation could be explained by the evasion of AGO1-57 from P0-mediated degradation or alternatively, that the mutation in AGO1 leads to constitutive activation of defense-related genes leading to enhanced resistance, as observed for TRV-infected ago1-27 (Ma et al , 2015), and regulated by miRNA and phasiRNA in multiple plant species (Li et al , 2012; Shivaprasad et al , 2012; Deng et al , 2018; López-Márquez et al , 2020). To discriminate between these two hypotheses, we performed similar infection kinetics in the three ago1 hypomorphic mutants used previously.…”