LAUSR

Polyploidization is an important feature of speciation that results from genome doubling. Tetraploid plants often have better physical characteristics than their diploid counterparts, and Paulownia is no exception. In our previous studies, several genes related to timber quality and abiotic stress resistance were identified in Paulownia tomentosa and Paulownia fortunei. However, the genes related to disease resistance and high biomass were not confirmed. In this study, small RNA and transcriptome sequencing were performed to analyze changes in microRNA (miRNA) and mRNA expression levels in tetraploid Paulownia tomentosa × Paulownia fortunei and Paulownia australis and their diploid counterparts. A total of 930 common differentially expressed genes and 66 (19 known and 47 novel) common differentially expressed miRNAs were detected in the two tetraploid vs. diploid comparisons. Twenty-two miRNA target genes were predicted, and the regulatory functions of the miRNA–target gene pairs were analyzed, of which the novel miR327- SGT1 HOMOLOG PROTEIN At5g65490 (PAU019930.1) and pau-miR2111a-MYB-RELATED TRANSCRIPTION FACTOR (PAU011118.1) interacting pairs were predicted to co-regulate disease resistance in tetraploid Paulownia. The pau-miR157i-SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 15 (PAU009402.1) and novel miR10-PUTATIVE PENTATRICOPEPTIDE REPEAT-CONTAINING PROTEIN At5g65820 (PAU012281.1) interacting pairs were predicted to co-regulate high biomass in tetraploid Paulownia. The expression trends of the miRNA and candidate target genes were validated by qRT-PCR. The results will help to accelerate genetic gain in Paulownia breeding programs to develop superior varieties.