Toward a Molecular Understanding of Rhizosphere, Phyllosphere, and Spermosphere Interactions in Plant Growth and Stress Response

Abstract The rhizosphere and phyllosphere are the below- and above-ground microbial ecosystems of plants. Interactions between the rhizosphere and phyllosphere shape the plant-microbiome environment, which carries out functions from seedling development to reproductive growth. The microbial community of germinating seeds and associated soil is termed the spermosphere. It represents the numerous microorganisms that, by modulating seed exudates, may impact the establishment of the rhizosphere and phyllosphere. In this review, we first explore the recent understanding of plant-microbe interactions in the rhizosphere and phyllosphere. Then, we outline the roles of the spermosphere in plant growth and stress response. The rhizosphere and phyllosphere offer complex routes for the recruitment of microbes, which ultimately affect the spermosphere. Notably, spermosphere microbial communities impact numerous aspects of seed biology, including seed development, dormancy, germination, storage, and dispersal. Environmental and genetic variables that influence rhizosphere, phyllosphere, and spermosphere interactions are also discussed. Plant health and agricultural production can be significantly improved by understanding rhizosphere, phyllosphere, and spermosphere interactions, and this knowledge can be used to optimize the composition and function of these ‘spheres’.