Abstract
Methyl jasmonate (MeJA) treatment elicits induced resistance (IR) against pests and diseases in Norway spruce (Picea abies). We recently demonstrated using mRNA-seq that this MeJA-IR is associated with both a prolonged upregulation of inducible defenses and defense priming. Gene expression can be regulated at both a transcriptional and post-transcriptional level by small RNAs, including microRNAs (miRNAs). Here we explore the effects of MeJA treatment and subsequent challenge by wounding on the Norway spruce miRNA transcriptome. We found clusters of prolonged down- or upregulated miRNAs as well as miRNAs whose expression was primed after MeJA treatment and subsequent wounding challenge. Differentially expressed miRNAs included miR160, miR167, miR172, miR319, and the miR482/2118 superfamily. The most prominent mRNA targets predicted to be differentially expressed by miRNA activity belonged to the nucleotide-binding site leucine-rich repeat (NBS-LRR) family. Among other predicted miRNA targets were genes regulating jasmonic acid biosynthesis. Our results indicate that miRNAs have an important role in the regulation of MeJA-IR in Norway spruce.
Highlights
Induced resistance (IR) is an important adaptation that allows plants to increase their resistance to herbivores and pathogens in response to a triggering stimulus (De Kesel et al, 2021)
We observed large-scale changes to the Norway spruce mRNA transcriptome in response to methyl jasmonate (MeJA) treatment and/or wounding challenge (Mageroy et al, 2020b)
In agreement with a previous study examining Small RNAs (sRNAs) expression in Norway spruce (Nystedt et al, 2013), we found that the majority of sRNAs in Norway spruce bark were 21 nt miRNAs, with a very low frequency of 24 nt sRNAs (Fig. 2)
Summary
Induced resistance (IR) is an important adaptation that allows plants to increase their resistance to herbivores and pathogens in response to a triggering stimulus (De Kesel et al, 2021). Prolonged upregulated defenses remain activated for long periods following the triggering stimulus, while primed defenses remain at basal levels until a secondary challenge elicits an augmented defense response (Wilkinson et al, 2019; Mageroy et al, 2020a). These two IR mechanisms are associated with different costs and benefits and the optimal strategy is dependent on the environment (Wilkinson et al, 2019).
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