Concentration-dependent regulation of growth and development by calliterpenone through hormonal crosstalk in...

Plant growth and development are governed by intricate hormonal networks that integrate environmental and endogenous signals. Plant growth regulators can be natural or synthetic chemical compounds that mimic hormonal regulation to alter plant growth and development. Here, we identify Calliterpenone (CT), a tetracyclic diterpenoid isolated from Callicarpa macrophylla, as a novel regulator of growth-defense balance in Arabidopsis thaliana. Phenotypic analyses revealed a clear concentration-dependent response, where low CT levels promoted seed germination, primary root elongation, vegetative growth, and early flowering, whereas higher concentrations inhibited root growth and shifted developmental outcomes. Cellular studies showed that CT regulates root elongation by modulating cell expansion, as evidenced by differential expression of expansin genes. CT also enhanced root hair density, indicating increased auxin responsiveness. Physiological measurements showed that CT improves photosynthetic efficiency, as evidenced by increased chlorophyll content, PSII efficiency, and gas-exchange parameters. Transcriptome profiling uncovered extensive reprogramming of genes involved in photosynthesis, metabolism, hormone signalling, and stress responses. Notably, CT modulated key flowering regulators through circadian and gibberellin (GA)-dependent pathways, enabling floral transition even under altered regulatory conditions. Hormonal analyses revealed that CT promotes GA accumulation at low concentrations, while higher levels induce auxin redistribution and jasmonic acid (JA) accumulation. Gene expression data further showed suppression of auxin biosynthesis but enhanced auxin transport and signalling, alongside a dynamic regulation of JA biosynthesis and turnover. Collectively, our findings demonstrate that CT orchestrates growth and defence by integrating GA-, auxin-, and JA-mediated pathways. This study highlights the potential of CT as a promising regulator for enhancing crop productivity and stress resilience in sustainable agriculture.