Physiological combined with transcriptomics analysis provided new insights into the enhanced Cd stress resilience of Ricinus communis L. via castor bean meal biofertilizer

Agricultural soil cadmium (Cd) contamination severely endangers the growth and yield of oil crops. Castor bean meal (CBM) biofertilizer integrates microbial and organic fertilizer properties to regulate plant growth by improving the soil microbial environment and supplying essential nutrients to crops. However, the molecular mechanism underlying CBM-mediated alleviation of Cd toxicity in castor ( Ricinus communis L.) remains unelucidated. This study aimed to elucidate the beneficial effects of 10 g·kg −1 CBM on alleviating Cd-induced toxicity (150 mg·kg −1 CdCl 2 ·2.5H 2 O) in 3-week-old castor seedlings. Through combined physiological, transcriptomic, and molecular analyses, exogenous CBM supply could enhance seedling growth by increasing chlorophyll accumulation, enhancing antioxidant system activity (encompassing enzymatic and non-enzymatic components), and reducing proline content. Additionally, transcriptomic analysis confirmed that genes involved in four key pathways-chlorophyll synthesis and degradation, proline metabolism, starch and sucrose metabolism, and the antioxidant system-play essential roles in CBM-mediated Cd resistance. Notably, the constructed castor gene regulatory network (CGRN) further identified key functional genes (e.g., SOD , POD , APX ) and transcription factors (TFs; e.g., MYB , Trihelix , HD-ZIP families) that likely mediate CBM-alleviated Cd toxicity in castor. Collectively, these results shed light on the mechanisms by which CBM fertilizer ameliorates Cd phytotoxicity and provide a theoretical basis for optimizing phytoremediation strategies.