Phytohormone and energy metabolism of rice germination and coleoptile growth during submergence by RNA-seq and LC-MS/MS analysis

Rice is one of the main food crops to guarantee the world's food security. Although rice is a semi-aquatic crop, long-term flooding stress can also inhibit growth and reduce yield and quality. Especially during the germination period, the germination rate of rice was inhibited by flooding stress, which resulted in the low emergence rate. Therefore, in this study, rice lines or cultivars with flood tolerance (C11) and flood sensitivity (KY60) were screened, and analyzed the response mechanisms during seed germination at different time points of waterlogging stress through transcriptome and metabolome sequencing. Compared with C11, waterlogging stress significantly inhibited the germination and coleoptile growth of KY60. Certain pathways, including plant hormones, energy metabolism, and carbohydrate metabolism, were identified as significantly involved in the flooding stress response in rice. The plant hormone-related DEGs (IAA, SAUR, ARF, LOX) and metabolites (IAA, JA, GA, and SA) were identified to up-regulate gene expression levels and significantly up-accumulate phytohormone content in C11 to resist waterlogging stress. However, the ABA signaling pathway-related genes (ZHD, PLY) and ABA content were decreased in C11 under submerged conditions. It is beneficial for C11 to promote seed germination and coleoptile elongation under flooding conditions. A total of 150 DEGs (AMY, PGLR) and 58 related compounds were identified as involved in the energy metabolism and carbohydrate metabolism of rice after flooding stress. Candidate key genes and metabolite compounds were identified by combined RNA-Seq and LC-MS/MS correlation network analysis. This study provided insights to explore the flood-tolerance mechanism of rice and laid the foundation for the cultivation of new varieties of flood-tolerance rice.