Mechanism of the Breaking of Seed Dormancy by Flower Thinning in Heracleum moellendorffii Hance

Abstract

As a non-wood forest product, Heracleum moellendorffii Hance, a traditional Chinese medicine and wild vegetable, plays a very important role in local forest protection and forest resource development. However, only a few physiological and biochemical studies have been conducted on H. moellendorffii, which has seed dormancy. Based on planting trials, flower thinning can not only promote seed production but also increase the germination rate. Therefore, it is necessary to study H. moellendorffii to better understand the relationship between flower thinning and seed dormancy. Determination of seed quality indexes was performed to evaluate the seed quality with and without flower thinning treatment. To further reveal the underlying biological processes, transcriptional analysis was performed based on the immature seed, naturally mature seeds, and naturally mature seeds with flower thinning treatment. After screening seed dormancy-related differentially expressed genes (DEGs), 220,841 unigenes were successfully confirmed including CYP, MYB, APX1, GRX, HSP, LEGA, LEGB, RFC1, HOX, PAP, MPA, and FATB. Furthermore, the transcriptional changes were discussed overall by GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses. The results showed that oxidoreductase activity, protein processing, alpha-linolenic acid metabolism, and fatty acid degradation were the main biological processes, and ACSL, ACOX1, ECHS1, and HADH are the candidate genes for these terms, respectively. Candidate gene expression was validated by qPCR. Flower thinning can promote the maturity of H. moellendorffii seeds, improve the seed quality, and break seed dormancy. Oil body proteins and fatty acid metabolism both played significant roles in the process of seed embryo development and seed dormancy release. In future applications, flower thinning may be an effective technique for the breaking of seed dormancy. This study provides a theoretical basis for the application of flower thinning to break seed dormancy.