Beneficial microorganisms are used to stimulate the germination of seeds; however, their growth-promoting mechanisms remain largely unexplored. Bacillus subtilis is commonly found in association with different plant organs, providing protection against pathogens or stimulating plant growth. We report that application of B. subtilis to melon seeds results in genetic and physiological responses in seeds that alter the metabolic and developmental status in 5-d and 1-month-old plants upon germination. We analysed mutants in different components of the extracellular matrix of B. subtilis biofilms in interaction with seeds and found cooperation in bacterial colonization of seed storage tissues and growth promotion. Combining confocal microscopy with fluorogenic probes, we found that two specific components of the extracellular matrix, amyloid protein TasA and fengycin, differentially increased the concentrations of reactive oxygen species inside seeds. Further, using electron and fluorescence microscopy and metabolomics, we showed that both TasA and fengycin targeted the oil bodies in the seed endosperm, resulting in specific changes in lipid metabolism and accumulation of glutathione-related molecules. In turn, this results in two different plant growth developmental programmes: TasA and fengycin stimulate the development of radicles, and fengycin alone stimulate the growth of adult plants and resistance in the phylloplane to the fungus Botrytis cinerea. Understanding mechanisms of bacterial growth promotion will enable the design of bespoke growth promotion strains.

使用有益微生物刺激种子发芽；然而，它们的增长促进机制在很大程度上仍未得到探索。枯草芽孢杆菌通常与不同的植物器官相关联，可提供针对病原体的保护或刺激植物生长。我们报告说，将枯草芽孢杆菌应用于甜瓜种子会导致种子发生遗传和生理反应，从而改变发芽后 5 天和 1 个月大植物的代谢和发育状态。我们分析了B. subtilis细胞外基质不同成分的突变体生物膜与种子相互作用，并发现在种子贮藏组织的细菌定植和促进生长方面的合作。将共聚焦显微镜与荧光探针相结合，我们发现细胞外基质的两种特定成分淀粉样蛋白 TasA 和 fengycin 不同地增加了种子内活性氧的浓度。此外，使用电子和荧光显微镜以及代谢组学，我们发现 TasA 和 fengycin 都靶向种子胚乳中的油体，导致脂质代谢和谷胱甘肽相关分子积累的特定变化。反过来，这导致两种不同的植物生长发育程序：TasA 和 fengycin 刺激胚根的发育，灰霉病。了解细菌生长促进机制将能够设计定制的生长促进菌株。