Genome-Wide Identification of miRNAs and Its Downstream Transcriptional Regulatory Network during Seed Maturation in Tilia tuan

Seed maturation not only determines the qualities and yields of seeds, but also affects seed storage and quality preservation. MicroRNAs (miRNAs) are a ubiquitous regulatory factor of gene expression in eukaryotes, which participate in the complex regulatory network of gene expression during seed maturation. However, miRNAs involved in maturation of Tilia tuan are still unknown. To reveal the role of miRNAs in T. tuan, small RNAs were profiled by high-throughput sequencing during seed maturation at five developmental stages. By predicting the target genes of miRNAs, the expression patterns of miRNAs during seed maturation were analyzed to identify those related to seed maturation. A total of 187 known miRNAs belonging to 42 miRNA families were found at five different seed maturation stages. Based on the analysis of unknown sequences, eight novel miRNAs were identified; 11,775 targets of 195 miRNAs were identified. Large numbers of miRNAs with diverse expression patterns, multiple-targeting and co-targeting of many miRNAs, and a complex regulatory network of miRNA-target genes were identified during seed maturation. These miRNAs and their targets may be involved in fatty acid, ABA, and lignin biosynthesis. Our study provides more information about the miRNA regulatory network and deepens our understanding of the function of miRNAs in T. tuan. miRNAs are revealed to be crucial during seed maturation, which provides a basis for further study of the regulatory role of miRNAs during seed maturation.