Molecular And Physiological Mechanism In Response To Gadolinium Stress Of Saccharomyces Cerevisiae And Oryza Sativa

The unreasonable exploit and utilization of rare earths has led to their massive accumulation in water and soil.Plants,animals,and microorganisms in rare earth contaminated areas are subjected to varying degrees of persecution,and human beings as the top organisms in the food chain are also seriously threatened.In this paper,gadolinium（Gd）,which is widely used in nuclear power,medical,and industrial fields,was selected as the stress factor,and Saccharomyces cerevisiae and Oryza sativa were used as the experimental materials to preliminarily explore the molecular and physiological response mechanism of organisms under the stress of Gd.The main results were as follows:A sub-lethal concentration of Gd was used as a stress factor to screen the diploid single-gene deletion strain library of Saccharomyces cerevisiae（there are 4741 gene deletion strains in this library）.Forty-five Gd-sensitive gene deletion strains and 10Gd-tolerant strains were obtained.Functional localization analysis indicated that these genes are involved in cell metabolism,cell cycle,transcription and translation,protein synthesis and folding,and cell transport.They are mainly located in the cytoplasm,Golgi apparatus,nucleus,and vacuole membrane.Further analysis via inductively coupled plasma mass spectrometry（ICP-MS）revealed that the content of Gd in 45 sensitive strains was higher than that in the wild type,which suggests that the sensitivity of yeast gene deletion strains may be related to excessive Gd uptake.Among the sensitive genes screened,four genes are involved in the regulation of calcium signaling pathway:CNB1encodes calcineurin（Ca N）regulatory subunit Cn B,CRZ1 encodes Ca N-dependent transcription factor,VCX1 encodes Ca²⁺/H⁺antiporter in vacuolar membrane,and GDT1encodes Ca²⁺/H⁺exchanger in Golgi membrane.Four other sensitive genes are involved in phosphorus metabolism,PHO2 and PHO4 encode transcription factors,which interact and co-regulate the transcription of genes involved in phosphorus deficiency,PHO84 encodes the high-affinity inorganic phosphate transporter,and PHO86 is involved in Pho84 vesicle transport.In addition,there are many genes involved in the protein sorting pathway:ARF1,ARL1,ARL3,SYS1,COG5,COG6,YPT6,VPS9,SSO2,MRL1,AKL1,and TRS85.The ion radius of Gd³⁺is similar to Ca²⁺.Gd³⁺may break the intracellular Ca²⁺homeostasis by competing for the Ca²⁺binding site,thereby interfering with the Ca²⁺signaling pathway and the sorting of related proteins regulated by the Ca²⁺signaling pathway.In addition,Gd³⁺easily combines with phosphate to form an insoluble phosphate in an inactive state,which leads to phosphorus deficiency in cells and breaks the balance of phosphorus metabolism,thus significantly inhibiting the growth of yeast.Further analysis using bioinformatics methods revealed that the 55 sensitive or tolerant genes screened had 52 homologous genes in humans and 32 homologous genes in rice.This points out the direction of further research on the toxicity of Gd to humans and rice.Rice is one of the most severely stressed crops by rare earth in China.Gd is one of the most widely used and polluted rare earth elements.Most studies focus on light rare earths,but research on heavy rare earths is rare.In addition,the mechanism of detoxification of plants under heavy rare earth stress has not been clarified.This study uses rice as a model plant to study the chemical forms and subcellular distribution of heavy rare earth Gd in rice.The nutrient absorption of rice roots and shoots under Gd stress were studied by ICP-MS.The chemical forms and subcellular distribution of rare earth Gd in rice were determined.This indicates the mechanism of rice absorption and detoxification in Gd stress.The following conclusions were obtained:Gd promoted rice root,shoot elongation and rice primary root growth at 1μM.When the concentration of Gd is higher than 10μM,it has an inhibitory effect on rice growth.The the concentration of Gd is higher,the inhibition is more obvious.At 1000μM Gd,the effect of inhibition was most pronounced.In addition,rare earth Gd can also break the dynamic balance of nutrient elements in rice.High concentration of Gd can significantly inhibit the absorption of K,Ca,Mn,Zn,Cu and Mo.The subcellular distribution of rare earth Gd in rice shows that the concentration of Gd in the cell wall,organelles,and soluble components is also increasing with the increase of Gd concentration.The percentage of Gd in the cell wall is higher than that of the organelle and the soluble component.The chemical form of Gd in rice shows that Gd is mainly present in the form of phosphate and oxalate in rice.The percentage of phosphate Gd increases with increase of Gd concentration,indicating that phosphate may be a specific means of immobilization and detoxification of Gd.Hierarchical clustering analysis indicated that rice seedlings could cope with Gd toxicity through cell wall compartmentalization as well as forming of precipitates with oxalate and phosphate.