Integrated Transcriptome and Metabolome Analyses Reveal the Mechanism Regulating Bulbil Initiation and Development in Cystopteris chinensis

Cystopteris chinensis is an endangered fern endemic to China, which only has a small wild population due to its poor reproductive ability. However, we recently found that it can produce bulbils on its pinnule to generate new plants but the molecular mechanism underlying this unique phenomenon remained unknown. In this study, we have identified four distinct stages in the initiation and development of bulbils based on morphological and anatomical observation. We performed transcriptome and metabolome analyses on the collected samples at each stage. Through KEGG enrichment analysis, it was found that the phytohormone signal transduction, starch and sucrose metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis pathways play a significant role in regulating bulbil initiation and development. Specifically, the involvement of three phytohormones and sugar substances was identified in the process of bulbil initiation. Our study provides the first detailed observation of the bulbils in C. chinensis and explains their initiation and development at the molecular level. However, more in-depth studies are needed to discover the functions of key genes controlling the formation of bulbils to conserve the endangered C. chinensis population.