Multi-omics and physiological traits analysis revealed the regulatory mechanism of selenium reducing cadmium toxicity in Desmodesmus abundans.

Cadmium (Cd) is a toxic non-essential heavy metal. Cd pollution has emerged as a serious environmental issue. Selenium (Se) is an essential trace element for human health. Scenedesmus has broad application prospects in remediating Cd-contaminated soil and wastewater treatment. The combination of Se and Scenedesmus is beneficial for reducing Cd and enriching Se in crops. However, it is not clear whether Se can alleviate Cd toxicity in Scenedesmus. In this study, Se significantly reduced cell death, reactive oxygen species, and proline content, while increased antioxidant levels in Desmodesmus abundans under Cd stress. Meanwhile, Se partially restored the biomass and chlorophyll fluorescence parameters of Desmodesmus abundans under Cd stress, indicating that Se mitigated the toxic impacts of Cd on the photosynthesis and growth in Desmodesmus abundans. Transcriptomic analysis revealed a series of differentially expressed genes involved in the response to Se and Cd stresses. Metabolomics analysis identified 169 differentially expressed metabolites, including antioxidants and flavonoids, which play important roles in Se mitigating Cd toxicity. Furthermore, rice cultivation experiments showed that combination of Se and Desmodesmus abundans alleviated Cd-induced inhibition of rice growth, achieving Cd reduction and Se enrichment in rice. The combination of 1 mg L Se and microalgae increased the rice shoot height by 57.35 % and Se content reached 17.18 μg g under Cd stress, while the Cd content of rice decreased by 53.59 %. This study advances the understanding of how Se mitigates Cd toxicity in microalgae and provides a feasible strategy for Se enrichment and Cd reduction in crops.