Dynamic expression of novel and conserved microRNAs and their targets in diploid and tetraploid of Paulownia tomentosa

MicroRNAs (miRNAs) play profound roles in plant growth and development by regulating gene expression. Tetraploid plants often have better physical characteristics and stress tolerance than their diploid progenitors, but the role of miRNAs in this superiority is unclear. Paulownia tomentosa, (Paulowniaceae) is attracting research attention in China because of its rapid development, wide distribution, and potential economic uses. To identify miRNAs at the transcriptional level in P. tomentosa, Illumina sequencing was used to sequence the libraries of diploid and tetraploid plants. Sequence analysis identified 37 conserved miRNAs belonging to 14 miRNA families and 14 novel miRNAs belonging to seven miRNA families. Among the miRNAs, 16 conserved miRNAs from 11 families and five novel miRNAs were differentially expressed in the tetraploid and diploid; most were more strongly expressed in the former. The miRNA target genes and their functions were identified and discussed. The results showed that several P. tomentosa miRNAs may play important roles in the improved traits seen in tetraploids. This study provides a foundation for understanding the regulatory mechanisms of miRNAs in tetraploid trees.