Transcriptomic analyses reveal molecular mechanisms underlying regulation of floral attributes in Lonicera japonica Thunb.

Abstract

Background Lonicera Japonica Thunb. is a perennial, semi-evergreen and twining vine in the family of Caprifoliaceae, which is widely cultivated in Asia. Thus far, L. japonica is often used to treat some human diseases including COVID-19, H1N1 influenza and hand-foot-and-mouth diseases, however, the regulatory mechanism of intrinsic physiological processes during different floral developmental stages of L. japonica remain largely unknown. Results The complete transcriptome of L. japonica was de novo-assembled and annotated, generating a total of 195850 unigenes, of which 84657 could be functionally annotated. 70 candidate genes involved in flowering transition were identified and the flowering regulatory network of five pathways was constructed in L. japonica. The mRNA transcripts of AGL24 and SOC1 exhibited a downward trend during flowering transition and followed by a gradual increase during the flower development. The transcripts of AP1 was only detected during the floral development, whereas the transcript level of FLC was high during the vegetative stages. The expression profiles of AGL24, SOC1, AP1 and FLC genes indicate that these key integrators might play the essential and evolutionarily conserved roles in control of flowering switch across the plant kingdom. We also identified 54 L. japonica genes encoding enzymes involved in terpenoid biosynthesis pathway. Most highly expressed genes centered on the MEP pathway, suggesting that this plastid pathway might represent the major pathway for terpenoid biosynthesis in L. japonica. In addition, 33 and 31 key genes encoding enzymes involved in the carotenogenesis and anthocyanin biosynthesis pathway were identified, respectively. PSY transcripts gradually increased during the flower development, supporting its role as the first rate-limiting enzyme in carotenoid skeleton production. The expression level of most anthocyanin biosynthetic genes was dramatically decreased during the flower developmental stages, consistent with the decline in the contents of anthocyanin. Conclusion These results identified a large number of potential key regulators controlling flowering time, flower color and floral scent formation in L. japonica, which improves our understanding of the molecular mechanisms underlying the flower traits and flower metabolism, as well as sets the groundwork for quality improvement and molecular breeding of L. japonica.