Screening Of Transcription Factor Involved In Rice Cd Absorption Regulation And Bioinformatics Analysis Of Related Gene Family

Heavy metal pollution is regarded as one of the most concerned environmental and food safety issues in recent years.Crops absorb Cd(Cadmium)form the Cd polluted soil,and high Cd containing crops seriously threat the health of human beings.To solve the Cd pollution,we could reduce the use of cadmium and replace the polluted soil.These methods require the huge investment and are highly time-consuming,resulting in a very low efficiency of solving Cd pollution.Cd-resistant crops are proposed by biologists as the way to reduce the Cd pollution.Through manipulating the transcription of genes and the expression of proteins,which are related to Cd absorption,transportation and storage,we may reduce the accumulation of Cd in the edible parts of crops.As a result,the agricultural products are safe to eat.Transcription factors are key players of regulating gene expression and responding to the environmental stimulus in plants.In this study after we screened transcription factors of rice,few of them,which may influence the accumulation of Cd in rice grain,have been unveiled and analyzed with bioinformatics tools.This research will be further described as the following two aspects:1.We planted 78 mutated rice samples,which contain mutations of 24 different transcription factors,and the kitaaki rice(wild type)in the Cd polluted soil(6.8mg Cd per kg soil).Then Cd content of grains from all samples after harvest was determined.We found that Cd content of kitaaki rice plants is high as 0.485mg/kg,2.5 times of the highest GB Cd content limitation(0.2mg/kg),implying that those rice samples exceed the safe standard seriously.In mutant strains,the Cd content of 4 strains(5%of the total mutants)have increased;the Cd content of 74 strains(95%of the total mutants)have decreased.Among them,there are 51 strains(66%of the total mutants)of 20 different transcription factors with Cd reducing rate higher than 30%.Besides,there are 8 transcription factors in which all their strains show Cd reducing rate higher than 30%,which belong to 3 different families,in which 5 of them belong to the bHLH family.The 9 strains of 8 transcription factors(12%of the total)with Cd content lower than GB limit,which means reducing rate is higher than 59%,belong to 5 different families,and 4 of strains belong to the bHLH family.The results suggest that the transcription factor,especially transcription factors of bHLH family,may affect the metabolism of Cd in rice.2.After analyzed the bHLH factors which could affect Cd metabolization,we got 9 bHLH genes.Their protein sequence and domain structure analysis result show that these genes are typical bHLH transcription factors,displaying the specific bHLH domain structure.We got 54 homo bHLH transcription factors by aligning the sequence of the 9 transcription factors.The analysis of system evolution shows that the 54 transcription factors belong to 7 different subfamilies,which occupies 34%of the bHLH subfamilies in rice and Arabidopsis thaliana.In addition,analysis of expression profiling of C family,I family,B family and X family shows that C family and B family belong to the constitutive expression;the members of I family are expressed in leaf and stem;the members of X family are highly expressed in seed.Meanwhile,the OsbHLH046,OsbHLH101 and OsbHLH168,the members with Cd content decreased obviously,belong to the C family;the OsbHLH066 also decreased Cd content obviously,which belongs to the I family;the OsbHLH099 decreased the Cd content relatively obviously,which belongs to X family,which refer to that the transcription factors may regulate the Cd metabolism in different tissues in rice.