Expression pattern analysis of microRNAs in root tissue of wheat (Triticum aestivum L.) under normal nitrogen and low nitrogen conditions

MicroRNAs (miRNAs) are highly conserved non-coding small RNAs involved in regulating plant growth and development, as well as plant responses, to diverse environmental signaling cues. In this study, the expression patterns of 38 wheat microRNAs (TaMIRs) were investigated under normal N and low N stress. Under normal N conditions, the TaMIRs exhibited four expression patterns: high, moderate, low, and undetectable expression. Seven TaMIRs (TaMIR156, TaMIR399, TaMIR444, TaMIR1118, TaMIR1129, TaMIR1133, and TaMIR1136) showed varied expression levels under N deprivation. TaMIR156, TaMIR444, TaMIR1118, TaMIR1129, and TaMIR1136 were upregulated, whereas TaMIR399 and TaMIR1133 were downregulated. The expression patterns of TaMIR444, TaMIR1118, and TaMIR1129 were further analyzed under various low N concentrations and then returned to normal N. The aforementioned TaMIRs exhibited ever higher expression at lower N concentrations and whose expressions returned to those before low N stress after they were restored to normal N conditions, which suggest that N concentration and low N-duration are inversely correlated with their expression. The putative target genes of the low N–responsive TaMIRs were identified and categorized into various functional groups. Expression analysis revealed that the target genes showed opposite pattern to that of their corresponding TaMIRs. Our results suggested that some low N–responsive TaMIRs are involved in regulating plant response to N deprivation by interacting with their target genes. Distinct TaMIRs are potentially involved in plant tolerance to low N stress through microRNA-mediated pathways.