Flooding represses soybean seed germination by mediating anaerobic respiration, glycometabolism and phytohormones biosynthesis

With global warming, flooding is becoming a serious natural abiotic stress in the past decades, which significantly influences plant growth and development, especially seed germination. However, the molecular mechanisms by which flooding stress represses land crop seed germination are largely unknown so far. Here, by using soybean (Glycine max), one of the most important oil crops worldwide, we report that flooding represses seed germination by mediating glycometabolism, anaerobic respiration and phytohormones biosynthesis related cascades. Phenotypic analysis showed that the flooding stress significantly decreases seed vigor and thus seed germination. Biochemical analysis demonstrated flooding leads to a decrease in several types of sugar contents during seed imbibition and an increase of cell conductivity as well as ethanol level, which remarkably inhibits seed germination. Subsequent transcriptomics and qPCR assays revealed that the expression levels of ABA (abscisic acid) and GA (gibberellin) biosynthesis/signaling and glycometabolism as well as anaerobic respiration related genes are consistent with the phenotypic and biochemical evidences. Furthermore, the exogenous sucrose or GA treatments can partially rescue the flooding or hypoxia-mediated repression of seed germination. Taken together, this study reveals that flooding stress impairs seed germination by decreasing sugar and phytohormones biosynthesis as well as promote anaerobic respiration.