QTL Mapping For Root Traits And Cadmium-Stress Tolerance In Wheat At The Seedling Stage

Wheat（Triticum aestivum L.）is one of the most important food crops in the world,and its quality and quantity safety are closely associated with the stability and development of our society.The quality and quantity of wheat are affected in many ways.The root system,one of the most essential organs of plants,assimilates water and materials from soil to supply wheat growth and thus plays a vital role in wheat production.In recent years,under the influence of human activities,cadmium pollution has become increasingly serious,severely impacting the safety of wheat production.The safety of food made from wheat has also been greatly threatened.Therefore,in this work,the exploration of QTL in regulating wheat root development and cadmium tolerance,as well as the screening of related candidate genes,will provide important gene resources for the further study of wheat root architecture and for the breeding of cadmium-tolerant wheat varieties.Compared to the landrace Chinese spring,there were significant differences in root traits and cadmium tolerance of the specific germplasm H461.Therefore,in this study,the RIL population（H461×CS,named as HCS population）constructed from H461 and CS was used to identify root phenotypes at the seedling stage under cadmium stress simulated by Cd Cl₂.Combined phenotypic data and the high-density genetic map constructed by 21197 effective SNP markers were used for QTL mapping.The important QTL was verified in the verification population（H461×CM107,named as HCM population）,and the candidate genes during the mapping interval were predicted by gene expression analysis and function annotations.The main results are as follows:1.Based on the phenotypic data of hydroponic root culture at the seedling stage and the high-density genetic map,two stable QTL were detected,and four candidate genes were predicted by gene expression analysis and gene function annotation in the interval,which provided a theoretical basis for the study of wheat root traits.The phenotypes of multiple root traits in the HCS population were measured in 4replicates under hydroponic conditions.The best linear unbiased prediction（BLUP）values of the four times were used in Pearson correlation analysis,and 19 pairs of significant or extremely significant correlations were detected,and the correlation coefficients ranged from 0.01 to 0.93.A total of 14 QTL related to wheat root traits at the seedling stage were identified combined with the genetic map and phenotypic data.Among them,two stable QTL were identified.One locus,QRD.sicau-3B,controlled root diameter,explaining 5.66-9.51%of phenotypic variation,and the other one,QRT.sicau-1B,controlled root tip number and explained 6.95-14.90%of phenotypic variation.Based on gene expression levels and function annotations analysis,homologous genes of Traes CS3B02G375100 and Traes CS3B02G382900,encoding two different enzymes,are involved in the formation of xylem in roots of Arabidopsis thaliana;so it is speculated that Traes CS3B02G375100 and Traes CS3B02G382900 are possible candidate genes for QRD.sicau-3B.It was found that the homologous genes of Traes CS1B02G256600 and Traes CS1B02G260000 participated in root nutrient uptake and development.Therefore,Traes CS1B02G256600 and Traes CS1B02G260000 were speculated to be candidate genes of QRT.sicau-1B.2.A stable new cadmium tolerant QTL（QRCRFW.sicau-1D）was detected under HCS population.Two candidate genes were predicted by gene expression analysis and function annotation,which provided a theoretical basis for molecular marker-assisted breeding of cadmium-tolerant wheat varieties.Based on the cadmium-responsive index,a new and stable cadmium tolerant QTL,named QRCRFW.sicau-1D,was identified in the HCS population,the physical interval was392.02-404.12 Mb and the LOD value was between 4.61 and 7.73,explaining 9.45-13.51%of phenotypic variation.A pair of KASP markers were successfully developed to detect QRCRFW.sicau-1D.The genotyping results combined with phenotypic data showed that QRCRFW.sicau-1D could significantly improve the cadmium tolerance of wheat by 19.88%under different genetic backgrounds.Based on the functional annotations in the QTL interval,both Traes CS1D02G293900 and Traes CS1D02G294000 could encode a zinc-like iron transporter.Previous studies indicated that zinc transporters might absorb and transport cadmium.Through RT-q PCR quantitative analysis,the expression of Traes CS1D02G293900 and Traes CS1D02G294000 in cadmium-sensitive material CS was significantly induced by cadmium treatment.In summary,Traes CS1D02G293900 and Traes CS1D02G294000 were inferred to be candidate genes for QRCRFW.sicau-1D.