Screening of Reference miRNA of Different Early- and Late-Flowering Tree Peony Varieties

miRNA plays an important role in plant growth and development and in response to various stresses. Quantitative real-time PCR (qRT-PCR) technology is often used to detect the expression level of miRNAs and genes by comparing with reference genes. In order to screen out the optimal reference miRNAs in different tree peony varieties, the petals of 42 different early- and late-flowering tree peony varieties were used as experimental materials, and geNorm, NormFinder, Bestkeeper, and RefFinder software were used to evaluate the stability of 16 candidate reference miRNAs. The results showed that the average Ct values of all candidate reference miRNAs were between 15.34 ± 0.29 and 32.64 ± 0.38. The optimal number of reference miRNAs was four, which were PsPC-5p-19095, PsPC-3p-51259, PsmiR159a, and PsPC-3p-6660 in geNorm. The stability of PsPC-3p-6660 was the highest in the analysis results of NormFinder software. Among the analysis results of Bestkeeper software, PsMIR319-p5 has the highest stability. Among the results of comprehensive evaluation and analysis of several software using RefFinder, the candidate reference miRNA with the highest stability was PsPC-3p-6660. When PsPC-3p-6660 was used as the reference miRNA, the expression of PomiR171 and PomiR414 in response to different flowering times of tree peony was relatively stable in 42 tree peony varieties, indicating that PsPC-3p-6660 was stable and reliable. The results of this study provide a reference miRNA for studying the expression changes of miRNA in different tree peony varieties and further exploring the regulatory mechanism of miRNA in different peony varieties.