Fructokinase OsFRK1 and OsFRK2 regulate seed germination associated with energy and ABA metabolism in rice

Fructokinase participates in carbohydrate metabolism via the phosphorylation of fructose and plays an important role in plant growth and development. In this study, we revealed the roles of the fructokinases OsFRK1 and OsFRK2 as positive regulators of seed germination and seedling growth by influencing abscisic acid (ABA) content and energy metabolism. Compared with the wild type (WT), the seed germination, seedling growth, and seed vigor of the osfrk1 and osfrk2 mutants were suppressed, with the osfrk1 mutants showing a larger inhibitory impact than the osfrk2 mutants. Energy metabolomics analysis indicated that OsFRK1 and OsFRK2 might be involved in the biosynthesis of secondary metabolites and carbohydrate metabolism to affect the energy required for seed germination. Furthermore, Ultra-High-Performance Liquid Chromatography Mass Spectrometer (UPLC-MS/MS) analysis demonstrated that the ABA content in the osfrk1 and osfrk2 mutants was significantly higher than in the WT. Reverse transcription quantitative PCR (RT-qPCR) results indicated that the expression of genes associated with ABA metabolism in the mutants was down-regulated. Additionally, exogenous ABA treatment showed that the osfrk1 and osfrk2 mutants exhibited heightened sensitivity to ABA during seed germination and seedling growth. Collectively, this work provides significant insights into the regulation of OsFRK1 and OsFRK2 on seed germination and vigor in rice, as well as theoretical references for practical problems such as the direct seeding of rice.