miRNA expression differentiation induced by polyploidization in newly formed triploids of black poplar

During whole genomic duplication (WGD) events, micro RNAs (miRNAs) are involved in stabilization of chromatin and genome and epigenetic regulation of gene expression. In this study, a newly induced triploid group of hybrids between sect. Tacamahaca and sect. Aigeiros in Populus, was characterized for genome-wide miRNA expression after WGD. Seven miRNA libraries (male parent, female parent, group of triploid offspring’s, group of diploid offspring, and three triploid individuals) were constructed and variation of miRNA expression from diploid parents to triploid offspring’s as well as distinction between triploid and diploid offspring were analyzed. The results showed that a total of 240 miRNAs were predicted including 187 known miRNAs and 53 novel miRNAs. 81.25% of miRNAs in triploid offspring were non-additively expressed in which 52.31% were down-regulated. A novel miRNA with 24nt in length choosing adenine as its first base was found in triploid offspring group suggesting its potential role in regulation of DNA methylation after WGD. A total of 18 novel miRNAs were specifically expressed in the library of triploid group. Targeted genes of different expressed miRNAs in three comparison sets (triploid offspring group vs female parent, male parent, and diploid offspring group) were all enriched in ADP binding (GO: 0043531; FDR < 0.05). KEGG enrichment pathway of all three comparison sets was plant-pathogen interaction. This study revealed an essential role of miRNAs involving in epigenetic regulation after WGD in poplar and provided a good model for further studies of polyploidization advantages in woody plant.