Linkage Analysis And Genome Wide Association Of Arsenic And Mercury Accumulation In Maize

With rapid development of industry and modern agriculture, a large number of farmland in the world has been contaminated by heavy metal. The heavy metal in the soil can accumulate in crops, posing a health threat to humans by the food chain. As one of grain crops, maize has the largest planting area in the world. Many researches showed that there were significant heavy metals absorption and accumulation differences in different maize varieties. The selection and breeding for maize varieties with low accumulation is considered a practical and cost-effective approach to minimize the influx of heavy metals into the human food chain, which can maintain the demand for safe corn and decrease the As content in As-contaminated soil simultaneously. It is the basis of cultivating low accumulation of varieties to screening germplasm resources with low accumulation as well as in-depth study the molecular mechanism of heavy metal accumulation and resistance.In the study, we used a linkage population and an association population with high genetic diversity as materials. The phenotype evaluation was conducted under multiple environments. The arsenic(As) and mercury(Hg) accumulation locis were detected by using the strategy which combine genome-wide association analysis and linkage analysis. The main results of this study are as follows:1. Using 230 elite inbred lines as materials, the plant materials were planted on two environments. Variance analysis showed the As and Hg concentrations for the five measured maize tissues in the RIL population were significantly affected by environment(E), genotype(G), and G×E factors. The As and Hg concentrations in different maize tissues followed the order: leaves >bracts >stems> axis>kernels.Some low accumulation materials were identified, which provide material foundation for breeding maize variety with low accumulation and genetic research.2. A population of 194 recombinant inbred lines derived from an elite hybrid Yuyu22, was used to identify quantitative trait loci(QTLs) for As and Hg accumulation attwo locations. Twenty-eight QTLs for As accumulatin were identified at two locations,mostly clustered in chromosomal bins 1.02–1.03, 1.07–1.08, 4.05, 5.03, 7.00,7.02–7.03, and twenty-three QTLs for Hg accumulation were detected, mostly clustered in chromosomal bins4.01,4.03,8.03,8.07,9.03-04. The detected potential chromosomal regions can be used for further analysis, which might represent targets for marker-assisted selection of maize cultivars with a low As or Hg content.3. Using 558,629 SNP makers for association population genotype, after analyzing of maker missing rate, minor allele frequency, 470,681 SNP were selected for future population structure analysis and association mapping. The mixed linear model with population structure and kinship was used for genome-wide association analysis. 151 associated SNPs(P < 0.0001) for As accumulation were found, located in 87 genes,55 of which have functional annotations; 143 associated SNPs(P < 0.0001) for Hg accumulation were identified, located in 78 genes, 56 of which have functional annotations.4. Comparing the results from association and linkage mapping, 13 common locis were associated with As accumulation and the candidate genes for 13 locis were F-box protein, ATP binding, isomerase activity, heat shock protein, protein binding,G-protein coupled receptor, oxidoreductase activity, catalytic activity, Transcribed locus, acyltransferase activity, electron carrier activity, DNA binding and hypothetical protein; 9 common locis were associated with Hg accumulation and the candidate gene for 9 locis were protein amino acid phosphorylation, regulation of transcription,scramblase family protein, ATP binding, transmembrane transport, response to stress,subtilisin-chymotrypsin inhibitor homolog1 and hypothetical protein. In addition, 4candidate gene for As accumulatioin and 5 candidate gene for Hg accumulatin were suggested for further study by gene function prediction.