Analysis of miRNA-mediated regulation of flowering induction in Lilium × formolongi

MicroRNAs play pivotal roles in plant vegetative phase change and flowering induction via integrating into multiple flowering pathways. Lilium × formolongi is an important ornamental lily cultivar that can flower within one year after sowing. However, it remains unresolved how miRNA-mediated regulation networks contribute to the L. × formolongi characteristics of a short vegetative growth period and rapid flowering.

In this study, the small RNA libraries and one degradome library were constructed for L. × formolongi during vegetative growth and flowering initiation, and 366 conserved miRNAs and 32 novel miRNAs were identified. Additionally, 84 miRNAs were significantly differentially expressed during development. A total of 396 targets of 185 miRNAs were identified and validated through degradome sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that functions of the targets were top enriched in the cold and cadmium ion responses, pentose phosphate pathway and carbon fixation in photosynthetic organisms. Furthermore, among 23 differentially expressed miRNA-target pairs, the miR156s-LfSPL2, miR172a-LfAP2 and miR164a-LfNAC pairs as well as miR159a-LfSPL2 were found to be relevant to flowering based on the correlation analysis of expression profiles in the miRNA libraries, degradome and transcriptome. A coexpression regulatory network focused on differentially expressed pairs was also constructed by WGCNA, and 14 miRNAs were considered putative key miRNAs during vegetative development and flowering induction. miR156a/ d/ e showed particularly strong relationships with other miRNAs in the coexpression network.

This study provides cues for the further exploration of the regulatory mechanisms of short vegetative development and flowering in L. × formolongi.