In the face of climate change, biodiversity loss and a rapidly growing population, global food security relies on improving agriculture production. However, it is equally crucial to limit or mitigate the environmental impact by developing sustainable and regenerative practices. Plant health strongly depends on plant-associated microbial communities, known as the microbiome, which can increase plant nutrient acquisition, tolerance to environmental stress, and resistance to diseases. Whereas most studies have focused exclusively on bacteria and, to a lesser extent, fungi, other plant-associated microbes like algae remain largely underappreciated in the plant microbiome. However, recent reports support that algae are ubiquitous in plant microbiomes and that (living) algae can improve plant fitness by promoting growth and increasing resistance against pathogens and abiotic stress. However, the underlying mechanisms of beneficial algal-plant interactions remain mostly unknown. Land plants evolved from a green algal ancestor and both, plants and algae, have co-evolved with interacting bacteria using similar mechanisms. Thus, algae, through their interactions with plant-associated bacteria, have the potential to influence the assembly and function of the microbiome itself. The AlgaeSphere project aims to uncover the overlooked potential of algal-bacterial interactions within the plant microbiome to improve plant growth in a circular bioeconomy model. By understanding the underpinnings of algal-bacterial interactions within the context of the plant microbiome, this project aims to reveal new players and emergent functions to improve the design of stable and higher-performing microbial consortia for sustainable agriculture and biotechnological applications for biofuel production and wastewater bioremediation.