Beyond elongation: The multifaceted roles of gibberellins in symbiosis and root development.

Plants regulate root development in response to fluctuating environmental conditions, including establishing symbiotic relationships with arbuscular mycorrhizal fungi and nitrogen-fixing bacteria under nutrient limitation. These processes are orchestrated by plant hormones, particularly gibberellins, and the repressors of gibberellin signalling, DELLA proteins. Gibberellin and DELLAs serve as critical regulators in symbiotic signalling and root organogenesis, integrating hormonal and environmental cues with cellular patterning to direct plant development. This review explores the current understanding of gibberellin and DELLA function in symbiosis and root development, including an analysis of the conservation and divergence of their function in land plant evolution. DELLA proteins play a pivotal role in the common symbiotic signalling pathway, modulating transcriptional responses essential for both arbuscular mycorrhizal and rhizobial symbioses. While gibberellin suppresses early symbiotic signalling and microbial infection by promoting DELLA degradation, gibberellin positively regulates nodule organogenesis and function, demonstrating a cell- and stage-dependent role in symbiotic associations. Indeed, precise spatial and temporal dynamics of gibberellin signalling occurs during nodulation and root development. Key avenues for future research are identified, including understanding how the crosstalk between gibberellin and other key plant hormones fine-tune symbiosis and root development.