Spermosphere Bacteria Promote Ormosia henryi Seed Germination by Activating Metabolic Pathways

Abstract

Spermosphere microorganisms are affected by seed exudates (carbon deposits) and interact with each other around the germinating seeds. The interactions in this region will have an important impact on seed germination, plant growth, and development. Ormosia henryi Prain is a rare and endangered tree species with hardseed in China that generally shows low levels of natural regeneration. However, good levels of natural regeneration were observed under a few mother trees in Guanling County (Guizhou Province, China). Based on this phenomenon: we raise the question: Is the seed germination of Ormosia henryi in high-level natural regeneration areas driven by the spermosphere microbe and what is the driving mechanism? The purpose of this study was to explore the promoting role of spermosphere bacteria in different stages of germination, so as to provide a theoretical basis for screening strong colonization ability spermosphere functional bacteria. Thus, in this study, we designed a germination experiment simulating the natural soil (sterilized and unsterilized) of Guanling County. We used 16S rRNA gene sequencing and widely targeted multiple reaction monitoring (MRM) metabolomic analysis to analyze bacterial microbial diversity and the metabolic profiles of seed exudates at the four stages of seed germination: imbibition, radicle protrusion, radicle elongation, and cotyledon protrusion. The results indicated that some spermosphere bacteria: taxa of Bacillus, Acidobacteriales, Nitrospira, and Ellin6067, and other functional bacteria may play important roles in promoting seed germination depending largely on their functional characteristics and abundance. The critical period for spermosphere bacteria to promote seed germination was at the radicle protrusion stage in the unsterilized soil group, levels of metabolites such as sugars and amino acids of seed exudates were increased in this stage, more respiratory pathways were activated and seed respiratory metabolism was enhanced. Spermosphere bacteria of wild Ormosia henryi in the Guanling area appeared to promote the germination of O. henryi seeds, mainly through activating galactose metabolism and the lysine degradation pathway to provide energy for germination.