miR825-5p targets the TIR-NBS-LRR geneMIST1and down-regulates basal immunity againstPseudomonas syringaein Arabidopsis

Abstract

Plants encode numerous intracellular receptors known as nucleotide-binding leucine-rich repeat receptors (NLRs) that recognize pathogen-derived effectors or their activity to activate defenses. MiRNA regulate NLR genes in many species, often triggering the production of phasiRNAs. Most such examples involve genes encoding NLR carrying coiled-coil domains, although a few include genes encoding NLRs carrying a Toll/interleukin-1 domain (TNL). Here, we characterize the role of miR825-5p in Arabidopsis, using a combination of bioinformatics, transgenic plants with altered miRNA levels and/or reporters, small RNA and virulence assays. We demonstrate that miR825-5p downregulates TNL MIST1 by targeting for endonucleolytic cleavage the sequence coding for TIR2, a highly conserved amino acid motif, linked to a catalytic residue essential for immune function. MiR825-5p acts as a negative regulator of basal resistance against Pseudomonas syringae. MiR825-5p triggers the production from MIST1 of a large number of phased siRNAs that can mediate cleavage of both MIST1 and additional TNL gene transcripts, potentially acting as a regulatory hub. MiR825-5p is expressed in unchallenged leaves and transcriptionally downregulated in response to PAMPs. Our results show that miR825-5p, which is required for full expression of PTI, establishes a link between PAMP perception and expression of uncharacterized TNL genes.

Functional Analysis of V2 Protein of Beet Curly Top Iran Virus

“…As BCTV V2, BCTIV V2 expression in a PVX heterologous system caused the induction of necrotic lesions in wt N. benthamiana , such as the ones produced during the HR, both at local and systemic levels in the wt N. benthamiana plants inoculated ( Figure 4 A,B). These results suggest that, in this PVX infection context, both proteins are avirulence factors that are directly or indirectly recognized by a resistance gene to trigger a defense response based on HR, known as effector-triggered immunity (ETI) [ 51 ]. It is remarkable that ectopic expression of BCTIV V2 from a 35S promoter did not cause any necrotic lesion in the infiltrated area in wt N. benthamiana leaves (similar results are observed when expressing BCTV V2) [ 16 ].…”

“…For high-molecular weight and small RNA Northern blots, total RNA was extracted using Trizol reagent (invitrogen) from the infiltrated leaves, and it was used for hybridizations as described ([ 50 ]). Probe labelling for U6 and GFP siRNA detection was performed, as described in ([ 51 ]).…”

An Overview of PRR- and NLR-Mediated Immunities: Conserved Signaling Components across the Plant Kingdom That Communicate Both Pathways

“…Furthermore, activation of PTI can upregulate the expression of a number of TNLs; however, such upregulation is dependent on Ca 2+ influx but not on ROS [ 145 ]. Finally, the overexpression of some of these PTI-induced TNLs resulted in increased defense outputs in Arabidopsis and N. benthamiana , suggesting that PTI triggers immune responses through TNL signaling pathways [ 99 , 147 , 148 , 149 ]. For a time, it was known that the EDS1-PAD4 complex was involved in basal immunity response, but the molecular mechanism was unclear [ 105 , 150 , 151 ].…”

New insight into the molecular mechanism of miR482/2118 during plant resistance to pathogens

“…In addition to targeting genes, it has been demonstrated that some miRNA-mediated cleavages of transcripts can trigger the production of phasiRNA ( Gai et al., 2018 ; Bélanger et al., 2020 ; López-Márquez et al., 2021 ; Shi et al., 2022 ). PhasiRNAs, another major class of small RNAs in plants, are involved in the control of plant biological processes ( Guo et al., 2018 ).…”