QTL Mapping And Candidate Genes Identification For Pb²⁺ Content In Different Maize Organs Under Lead Stress

Maize is not only the food crop with the largest acreage in the world, but also the important source material for industry, feed and deep processing of agricultural products, and its quality security is closely related to national health. Due to the rapid development of manufacturing and mining industry, Lead(Pb2+) enter into soil through continuous transport and deposition, causing serious heavy-metal contamination in the soil and bring about severe hazards to human being, plants and animals. In China, especially the southwestern region, the heavy-metal(Pb2+) contamination has been already extremely serious and some severely polluted regions are not suitable for agricultural cultivating, which restrict the development of agriculture and improvement of peasants’living standard in these regions, thus, how to reduce the Pb2+ content in soil and edible part of maize is our urgent problem. Owing to advantages including large biomass in ground parts, mechanically cultivating and strong heavy-metal phytoremediation ability in soil, conducting studies for Pb2+ absorption and enrichment characteristics, especially the genetic variation characteristic, is an important and effective way to solve problems of heavy-metal contamination in soil and food security. Recently, primary studies of QTLs related to heavy-metal absorption and enrichment in different crops were conducted, whiel the studies about QTLs of maize were rare. In this study, the IBMsyn10 DH population containing 215 lines constructed by B73 and Mo17 was employed as the experimental material, by employing the soil-pot cultivating method, the phenotype identification was conducted in 2013; after that, on the basis of combining the phenotype data with the previously constructed high density genetic map bin map, the QTL mapping was conducted for traits of Pb2+ content in maize root, stem, leaf and kernel via composite interval mapping (CIM) method, QTLs related to Pb2+ absorption and enrichment in maize were identified, then candidate genes were further identified by bioinformatics method to discuss the genetic and molecular mechanism controlling Pb2+ content in different maize tissues, as well as predict effective pathways regulating Pb2+ absorption and enrichment among different maize tissues, so as to provide theoretical foundation and material support for conducting MAS breeding and improving current materials in molecular level by genetic engineering technology in the future. The results are as follows.1. According to the statistical analysis result of Pb2+ content in root, stem, leaf, kernel of IBMsyn10 DH population and parent strains, the Pb2+ content in root, stem, leaf, and kernel of male parent Mo 17 and female parent B73 were significantly different, the Pb2+ content in root of Mo17 was 36.29 higher than that of B73, while Pb2+ contents in other tissues were significantly lower than the corresponding contents in B73. In IBM syn10 DH population, the Pb2+ contents in different tissues ranked as root>leaf>stem>kernel. Meanwhile, Pb2+ contents in different tissues were significantly different, and showing heterobeltiosis.2. Based on the IBMsyn10 DH population bin map previously constructed by our research team, a genetic linkage map containing the genotype of 215 lines was reconstructed. This genetic map consisted of 6359 bin markers in 10 chromosomes,, and covering a totla genetic distance of 4554.31 cM, the lengths of chromosomes ranged from 272.05 cM-724.42 cM, and the distances between adjacent markers ranged from 0.03 cM to 20.60 cM with an average distance of 0.72 cM.3. QTL mapping was conducted for Pb2+ content in different tissues, identifying 29 QTLs related to Pb2+ content. Among the 29 detected QTLs,8 were related to Pb2+ content in root, and the phenotype contribution rates ranged from 2.53% to 10.02%; 6 were related to Pb2+ content in stem, and the phenotype contribution rates ranged from 2.54% to 5.94%; 10 were related to Pb2+ content in maize leaf, and the phenotype contribution rate ranged from 4.64% to 12.79%; 5 were related to Pb2+ content in maize kernel, and the phenotype contribution rates ranged from 4.82% to 18.88%.4.8 candidate genes related to Pb2+ absorption or tolerance were screened out from QTLs confidence intervals.4 candidate genes related to Pb2+ content in maize root were located in Chr10; the biological function of GRMZM2G122437 may be encoding a kind of heavy-metal detoxify or transport family proteins, and that of GRMZM2G032293 may be encoding a kind of cation excretion protein, GRMZM2G021802 may encode a kind of heavy-metal related domain protein, GRMZM5G858653 may encode a kind of hydroxysuccinic acid transport protein.2 candidate genes related to Pb2+ transport in leaf were located in chr2, the biological function of AC233895.1_FGT001 may be encoding a kind of metallopeptidase, GRMZM2G088669 may encode a kind of heayv-metal transport or detoxify family proteins.2 candidate genes related to Pb2+ transport in kernel were located in Chr5, GRMZM2G336783 may encode a kind of ZIP-related heavy-metal transport family proteins, GRMZM2G386273 may encode a kind of ZIP transcript domain protein.