Identification Of Germplasms And Fine Mapping Of Quantitative Trait Loci For Aluminum Tolerance In Soybean

Aluminum?Al?toxicity is one of the major factors affecting soybean production in the region of Southern China.Therefore,it is of great significance to molecular marker-assisted and transgenic breeding on the base of mapping the aluminum-tolerant QTLs or genes by combinations of identifications on soybean germplasm as well as sequencing technology.In this study,a total of 139 different world-wide soybean germplasms were screened for the aluminum-tolerant genotypes by measuring method of relative root elongation?RRE?;Moreover,a F₁₁ advanced recombinant inbred line population derived from the cross of Zhonghuang 24×Huaxia 3?ZHX3?was adopted for QTL mapping.Two kinds of phenotypic data of relative root elongation?RRE?and apical Al content?AAC?were used to finely map QTLs of root associated aluminum-tolerant traits.Furthermore,in order to identify candidate genes that may regulate and control Al resistance in soybean,the quantitative expression of the genes were further detected among the genetic intervals of QTLs.The main conclusions are shown as follows:Soybean germplasms were screened for the phenotypic values of RRE using the seedling hydroponic culture with a certain concentration of Al solution treatment.The results showed that there were genotypic distinctions on aluminum tolerance of different materials and the variances of RRE presented a wide span?28%-113%?with the mean value up to 65%shown as a normal distribution model.In this study,we took the RRE more than 80%as the tolerance criterion and set the tolerant cultivar PI416937 as the control.A total of 31 resistant germplasms were identified including ZDD16505,Fudou 3,Nandou 8,Fendou 98 and Huaxia 3.Correspondingly,the standard for sensitive phenotype was 40%and 11 sensitive germplasms were pertained to this set.While two cultivars of Qidou 16 and Zheng 196 showed relatively extreme sensitive values with RREs less than30%.In this study,ZHX3 RILs and their two parents were also investigated by valuing RRE and AAC.The phenotypic data detected in ZHX3 population fitted skew normal distribution models with typical quantitative genetic characteristics.The correlation analysis between RRE and AAC turned out to be significantly negative?P<0.01?.The composite interval mapping?CIM?method was carried out to fine mapping analysis,based on a constructed high density genetic map using ZHX3 population.We finely mapped five QTLs for the traits of RRE and AAC.Three were three QTLs?qRRE₀4,qRRE₁6 and qRRE₁7?for RRE with the phenotypic effect variance?R²?by 7.09%-8.52%.Two QTLs of qAAC₀4 and qAAC₁9 were identified for AAC with phenotypic effect variance 8.98%and 7.26%,respectively.The comprehensive genetic effects of RRE and AAC was up to39.65%.The result of qRRE₀4 and qAAC₀4 detected by the same bin marker on chromosome 04 indicate new QTLs were found for soybean root Al-tolerance.A total of 66 predicted genes were contained in the genetic intervals of the five QTLs by looking through the database of NCBI and Soybase.By using RT-PCR to test gene responses to Al stress,fifteen genes were verified of different expression levels with the comparison between the Al treatment and the control.Finally,based on the functional annotations as well as former studies on these genes,we predicted there are nine putative candidate genes responsed to abiotic stress which contribute to Al tolerance including Glyma.04g218700,Glyma.04g218400,Glyma.04g220600,Glyma.04g217400,Glyma.04g213300,Glyma.04g214000,Glyma.04g216100,Glyma.04g218300 and Glyma.16g043300.