Insights into drought stress response mechanism of tobacco during seed germination by integrated analysis of transcriptome and metabolome

Drought stress inhibits seed germination, plant growth and development of tobacco, and seriously affects the yield and quality of tobacco leaves. However, the molecular mechanism underlying tobacco drought stress response remains largely unknown. In this study, integrated analysis of transcriptome and metabolome was performed on the germinated seeds of a cultivated variety K326 and its EMS mutagenic mutant M28 with great drought tolerance. The result showed that drought stress inhibited seed germination of the both varieties, while the germination rate of M28 was faster than that of K326 under drought stress. Besides, the levels of phytohormone ABA, GA19, and zeatin were increased by drought stress in M28. Five vital pathways were identified through integrated transcriptomic and metabolomic analysis, including zeatin biosynthesis, aspartate and glutamate synthesis, phenylamine metabolism, glutathione metabolism, and phenylpropanoid synthesis. Furthermore, 20 key metabolites in the above pathways were selected for further analysis of gene modular-trait relationship, and then four highly correlated modules were found. Then analysis of gene expression network was carried out of Top30 hub gene of these four modules, and 9 key candidate genes were identified, including HSP70s, XTH16s, APX, PHI-1, 14-3-3, SCP, PPO. In conclusion, our study uncovered some key drought-responsive pathways and genes of tobacco during seeds germination, providing new insights into the regulatory mechanisms of tobacco drought stress response.