Transcriptome and Metabolome Analyses Reveal Novel Insights into the Seed Germination of Michelia Chapensis, an Endangered Species in China

Abstract

Michelia chapensis Dandy, a well-known medicinal woody plant endemic to China, is endangered and seriously constricted by seed dormancy induced low-regeneration in natural conditions. Cold stratification can effectively release the seed dormancy and promote the seed germination of M. chapensis. However, the molecular biological events and systematic changes occurring in the seed germination of M. chapensis still remain unknown. In this study, the transcriptomic and metabolomic analyses and the profile observation were performed to learn the potential molecular mechanism of M. chapensis seed germination. The results showed that the embryo cells became larger and looser with the increasing stratification time. Moreover, the endosperm appeared reduced due to the consumption of nutrients. Seventeen phytohormones were examined by the metabolome targeted for hormones. Compared with the ES (no stratification), the levels of indole-3-acetic acid (IAA) and gibberellin A3 (GA3) were increased in the MS (stratification for 45 days), while the abscisic acid (ABA) was down regulated in both MS and LS (stratification for 90 days). The transcriptome profiling identified 24975 differentially expressed genes (DEGs) in the seeds during germination. The seed germination of M. chapensis was mainly regulated by the biological pathways of plant hormone signal transduction, energy supply, secondary metabolite biosynthesis, photosynthesis-related metabolism and transcriptional regulation. This study reveals biological evidence of the seed germination at transcriptional level, and provides a foundation for unravelling molecular mechanisms regulating the seed germination of M. chapensis.

Keywords: Michelia chapensis, Seed germination, Plant hormone signal transduction, Starch and sucrose metabolism, Energy supply, Biosynthesis of secondary metabolites