Enhanced resistance to bacterial and oomycete pathogens by short tandem target mimic RNAs in tomato

Abstract

SignificancePlants, like animals, have complex disease resistance systems in which receptors interact directly or indirectly with effectors of disease produced by pests and pathogens. To minimize the fitness cost of these systems to the plant, there are miRNAs that target the mRNAs of a family of receptor proteins required for disease resistance. Target site mimics of these miRNAs confer enhanced quantitative resistance in tomato against an oomycete and a bacterium. These findings are consistent with a role of the receptor proteins in quantitative disease resistance and show how blocking these miRNAs could be a useful approach in crop protection.

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

“…Previous reports on miRNA-mediated regulation of CNLs have highlighted the role in lowering the cost of surveillance of miRNA-mediated regulation of CNLs, but these have also shown these miRNAs have a potential role in lowering the cost of defense [34, 35]. Our results support miR825-5p is involved in repressing TNL expression in basal, unchallenged, conditions and potentially be thus involved in lowering the cost of surveillance.…”

“…The cost of surveillance is measured in the absence of disease and has been established in Arabidopsis for two R genes: RPS5 and RPM1 in [15, 17]. MiRNA-mediated regulation of NLRs has been proposed to act mainly by lowering the cost of surveillance, keeping down the expression of regulated R genes, and preventing accidental activation of their expression in the absence of a pathogen threat [34, 35]. Among the miRNA demonstrated to regulate expression of NLRs, 22nt miRNAs seem to be key elements, since they have the potential to establish a wider suppression of the resistance genes by triggering the production of secondary siRNA from primary target genes.…”

“…The fact that RDR6 is down regulated during PTI and that rdr6 mutants present stronger ROS and callose deposition upon flagellin treatment and are primed for expression of PTI marker genes [34], strengthens the significance of this mechanism in plant immunity. NLRs have been classified as phasiRNA or phasiNLR-producing loci when 10 or more 21-22 nt phased siRNAs accumulate from its sequence [35]. Whereas numerous CNL genes have been shown to give raise to accumulation of phasiNLRs in many plant species, just a few examples of sRNA accumulation have been reported for TNL genes [23,26,33–36,66].…”

“…On this note, AT5G18360, a putative primary target for miR825-5p, has been recently identified as a TNL involved in triggering ETI against Pto DC3000 effector HopB [79]. As proposed in tomato [35], miR825-5p may have a quantitative contribution to plant defenses, perhaps controlling low-level recognition of pathogen effectors in the absence of proper ETI. Further work will be necessary to characterize the role of the numerous TNL genes belonging to the miR825-5p regulon.…”

“…The members of the miR482/2118 families are probably the best characterized and have been identified in several plant species. Several miRNA families, including miR482/2118, trigger phasiRNA production mainly by targeting the NLR gene sequences encoding the P-loop motif, a well-conserved amino acid motif present in the NB-ARC domain of multiple NLRs from Arabidopsis , poplar, tobacco and tomato [33–35]. Mutation of a conserved residue within the P-loop results in loss of function of many plant NLRs [3].…”