interkingdom

Interkingdom refers to biological interactions that occur between organisms from different biological kingdoms, such as bacteria, archaea, fungi, plants, animals, and protists. The term encompasses communication, symbiosis, competition, and pathogenesis that cross traditional kingdom boundaries. Interkingdom signaling often involves chemical mediators, including small molecules, hormones, metabolites, and sometimes RNA-based signals that influence gene expression or behavior across species and kingdoms.

Common examples occur across ecosystems. In agriculture, plant roots interact with soil microbes in symbiotic relationships that aid nutrient uptake and defense, such as rhizobia with legumes or mycorrhizal fungi with various plants. In animal systems, gut microbiota communicate with host tissues to shape digestion, immunity, and metabolism. In aquatic and terrestrial environments, interkingdom interactions help regulate nutrient cycling and community structure through signaling between bacteria, fungi, algae, and plants. Cross-kingdom signaling also includes cases where microbial molecules affect plant or animal hosts and, conversely, plant or host signals influence microbial communities.

Research on interkingdom interactions employs methods such as metagenomics, metatranscriptomics, metabolomics, and imaging, alongside cross-culturing and functional assays. Network analyses and experimental perturbations help reveal how cross-kingdom relationships influence health, development, disease, and ecosystem function.

The concept has implications for agriculture, medicine, ecology, and biotechnology. It highlights the interconnected nature of life and supports efforts to manipulate microbiomes, improve crop resilience, and better understand host–microbe dynamics. Term usage varies, with some authors preferring cross-kingdom signaling or cross-kingdom interactions.