Identification and functional analysis of LpNAC37 associated with somatic embryogenesis in Lilium pumilum DC. Fisch. based on transcriptome analysis

Abstract

Somatic embryogenesis (SE) is important for Lilium bulb propagation, germplasm conservation, and genetic transformation. The transition of somatic cells to embryonic cells is a critical step in SE, but the associated regulatory mechanisms have not been fully elucidated. Lilium pumilum DC. Fisch has a high regenerative capacity, and this study clarifies the critical timing of embryonic cell appearance in Lilium SE. Transcriptome sequencing using RNA-seq technology was performed on 5 representative samples from the early stage of Lilium SE. The 15 established cDNA libraries yielded 91.47 GB of valid data, and a total of 11,155 genes were consistently differentially expressed in the early stages of Lilium SE. GO annotation and KEGG pathway analysis of differentially expressed genes (DEGs) suggested that transcriptional regulation, hormone signaling, and stress response pathways play essential roles in the early stages of Lilium SE. WOX8, WOX11, SHR2, NAC37, AHP2, ANT, PIN1C, LAX2, LBD4, ACS12, YUC4, NFYB3, WRKY28, SAUR50, PYL9, and WRKY39 may be candidate genes for regulating early SE in Lilium. We further cloned LpNAC37, one of the key DEGs obtained from WGCNA and screening. LpNAC37 encodes a protein of 303 amino acids with a conserved NAM structural domain. The protein is a nuclear transcription factor with the highest homology to carrot DcNAC37. Overexpression of LpNAC37 suggested that LpNAC37 promotes embryonic callus formation in Arabidopsis. These results will help reveal the molecular mechanisms of the early stages of Lilium SE and advance the application of SE in Lilium propagation and genetic transformation.

Keywords: Lilium; NAC; Somatic embryogenesis; Transcription factors; Transcriptome.