Comprehensive analysis of small RNA, transcriptome, and degradome sequencing: Mapping the miRNA-gene regulatory network for the development of sweet potato tuber roots.

As an important starch crop, sweet potato has significant practical importance for maintaining food security worldwide. This study identified differential expressed genes associated with the expansion of tuberous roots by comparing the transcriptome across tuberous roots at the initial period (initiated tuberous roots (ITRs), rapid expansion period (tuberous roots (TRs), fibrous roots (FRs) at the seedling stage, and fibrous roots at the adult stage (unexpanded FRs (UFRs)). sRNA-seq and degradome analyses were performed to reveal the role of miRNAs in tuberous root development in sweet potato. A total of 29,633 genes and 510 miRNAs were differential expressed among FRs, ITRs, TRs, and UFRs. Integrated analyses of these data revealed genes involved in metabolism, hormone response, and signal transduction that might participate in the induction of tuberous root formation, while genes involved in carbohydrate and energy metabolism that might participate in the tuberous root swelling. A joint analysis of miRNAs and DEGs related to tuber development revealed by degradome-seq identified twelve miRNA-target gene pairs involved in gene expression process, hormone response, and metabolism of secondary metabolites that might be key regulators of root tuber development in sweet potato. Moreover, the functions of many miRNA-target gene pairs involved in the initiation of root tuber were related to auxin signaling response, and an exogenous hormone treatment experiment was further performed. The results indicated that auxin treatment had the most significant effect on increasing sweet potato yield, suggesting a dominant role of the auxin pathway in the regulation of sweet potato tuberous root development. Additionally, two miRNA-target pairs, miR319-TCP4 and miR172-AP2, which were identified from the degradome, were verified via 5' RNA ligase-mediated rapid amplification of cDNA ends (RLR-RACE) and tobacco transient cotransformation tests, and their expression was impacted by auxin treatment, which further validated the reliability of our multiomics analysis results. Our research provides new insights into the role of miRNAs in sweet potato root tuber development.