Abstract
BackgroundNB-LRR resistance proteins are involved in recognizing pathogens and other exogenous stressors in plants. Resistance proteins are the first step in induced defence responses and a better understanding of their regulation is important to understand the mechanisms of plant defence. Much of the post-transcriptional regulation in plants is controlled by microRNAs (miRNA). We examined the expression of five Norway spruce miRNA that may regulate NB-LRR related transcripts in secondary phloem (bark) of resistant Norway spruce after wounding and inoculation with the necrotrophic blue stain fungus Ceratocystis polonica.ResultsThe plants of this clone recovered from both the pathogen inoculations and wounding alone. We found local and systemic induction of the resistance marker genes PaChi4, PaPAL and PaPX3 indicative of an effective induced host defence response. There were minor local and systemic changes in the expression of five miRNAs and 21 NB-LRRs between healthy and treated plants. Only five putative NB-LRRs (PaLRR1, PaLRR3, PaLRR14, PaLRR15 and PaLRR16) showed significant increases greater than two-fold as a local response to C. polonica. Of all NB-LRRs only PaLRR3, the most highly differentially regulated NB-LRR, showed a significant increase also due to wounding. The five miRNAs showed indications of an initial local and systemic down-regulation at day 1, followed by a later increase up to and beyond the constitutive levels at day 6. However, the initial down-regulation was significant only for miR3693 and miR3705.ConclusionsOverall, local and systemic expression changes were evident only for the established resistance marker genes and PaLRR3. The minor expression changes observed both for the followed miRNAs and their predicted NB-LRR targets suggest that the expression of most NB-LRR genes are maintained close to their constitutive levels in stressed and healthy Norway spruce plants.
Highlights
nucleotidebinding site and leucine-rich repeat (NB-LRR) resistance proteins are involved in recognizing pathogens and other exogenous stressors in plants
The minor expression changes observed both for the followed miRNAs and their predicted NB-LRR targets suggest that the expression of most NB-LRR genes are maintained close to their constitutive levels in stressed and healthy Norway spruce plants
The first level is induced by the recognition of conserved microbial molecules called pathogen associated molecular patterns (PAMPs) by cell surface located pattern recognition receptors (PRRs) that induce PAMP triggered immunity (PTI)
Summary
NB-LRR resistance proteins are involved in recognizing pathogens and other exogenous stressors in plants. We examined the expression of five Norway spruce miRNA that may regulate NB-LRR related transcripts in secondary phloem (bark) of resistant Norway spruce after wounding and inoculation with the necrotrophic blue stain fungus Ceratocystis polonica. Plant immunity is considered to rely on two major levels of resistance[3 and references therein]. Host-adapted pathogens evolve effectors (AVRs) that counteract PTI [3]. Host plants may utilize the second level of resistance known as effector triggered immunity (ETI), to recognize and counteract the effectors from adapted pathogens. Most ETI receptors are resistance proteins with nucleotidebinding site and leucine-rich repeat (NB-LRR) domain. TIR-NB-LRRs rust resistance proteins are involved in recognizing effectors from pathogenic rust triggering ETI in a gene-for-gene specific manner[3,5]
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