Hormones and chemical signals are key in regulating virtually all aspects of plant life. Recently, we have shown that zaxinone, a carotenoid-derivative, is a candidate for a novel plant hormone required for normal rice growth and development. A zaxinone synthase-1 (ZAS-1) loss-of-function mutant showed retarded growth, reduced grain yield, enhanced production of the plant hormone strigolactone (SL), and decreased symbiosis with arbuscular mycorrhizal fungi. Zaxinone supplementation partially rescued these mutant phenotypes and also enhanced root growth and decreased SL production in wild-type. Zaxinone is also released by rice roots, indicating a role in rhizospheric interactions beyond mycorrhization. Transcriptomic and metabolomic studies indicated that zaxinone promotes root growth by increasing sugar uptake in roots and modulating cytokinin homeostasis, and unraveled candidate genes for zaxinone metabolism, transport and response. Here, we aim at gaining deeper insights into the biology of zaxinone by investigating its metabolism, transport, perception and biological functions within and outside plants. We will functionally characterize rice ZAS-1 homologs and zaxinone-regulated genes presumably involved in its metabolism, transport and response, using enzymatic in vitro assays, transient expression in tobacco and rice protoplasts, and UPLC-MS. Furthermore, we will generate CRISPR-Cas9 mutant and overexpressing lines of promising genes, phenotype obtained lines and characterize them at cellular, transcriptomic and metabolomic level. For conversion and transport studies, we will perform feeding experiments with 13C-labelled zaxinone and fluorescent derivatives and synthesize candidate metabolites. To elucidate the role of zaxinone in plant-microbe communication, we will characterize mycorrhization and rhizomicrobiota of mutants, particularly ZAS and transporter mutants, and determine the metabolome of their root exudates. Finally, we will perform Genome-Wide Association Studies (GWAS), to identify additional candidate genes mediating zaxinone response and metabolism, and use LC-MS-based proteomics to find zaxinone binding proteins/receptor. Taken together, this project will significantly increase our knowledge about fundamental processes that govern growth and development, grain yield, mycorrhization and other interactions with soil microbes in the major crop rice. Furthermore, it has a large application potential, as it will provide novel targets for breeding rice with improved performance and nutrient uptake efficiency and unravel new regulatory metabolites promoting growth and beneficial biotic interactions.