Mapping Quantitative Trait Locus For Low Cadmium Accumulation In Brown Rice And Related Traits

Rice has a strong ability to accumulate cadmium（Cd）.Cd contaminated rice caused by farmland Cd pollution has been a social concern,and does harm to human body by food chain.It is important to excavate key genes controlling Cd concentration in brown rice for breeding low Cd-accumulating rice and ensure food safety.In this study,F₇ recombinant inbred line（RIL）population was constructed by a stable low Cd-accumulating rice D62B as the male parent and a high Cd-accumulating rice Wujin4B as the female parent.Quantitative trait locus（QTL）mapping of Cd accumulation related traits was conducted through field and hydroponic experiments,and stable QTLs controlling Cd accumulation related traits in rice were obtained,which can provide a theoretical basis for excavating genes regulating Cd accumulation in brown rice and selecting low Cd-accumulating rice by relevant molecular marker.The main results were as follows:（1）In the Cd contaminated soil,Cd concentration in different organs of D62B and Wujin4B showed as root>stem>leaf>brown rice.Cd concentration,Cd accumulation,and Cd translocation factor from root to stem,stem to leaf and leaf to brown rice of D62B were lower than those of Wujin4B under Cd stress.When exposed to different Cd doses,Cd concentration in brown rice of D62B was below 0.20 mg kg^-1,which satisfied the limitations of the National Food Safety Standard（GB 2762-2022）.（2）A total of 1250.72 G of high-quality available data were obtained through genome re-sequence.The average comparison rate of 187 rice materials was 98.30%compared with the reference genome,and the average sequencing depth was 17.31X.The average proportion of bases with a mass value greater than 20 is 97.54%,and the average proportion of bases with a mass value greater than 30 is 93.92%.A genetic linkage map covering 12chromosomes was constructed and the total length was 1745.70 c M.The map contained 785SNP bin markers with an average distance of 2.26 c M between adjacent molecular markers,and the proportion of less than 5 c M gaps on each chromosome was above 88%.（3）A total of 44 QTLs related to Cd accumulation were obtained by two field experiments with different levels of Cd contamination and a hydroponic experiment,including 6 QTLs controlling brown rice Cd concentration,4 QTLs controlling root Cd concentration,17 QTLs controlling shoot Cd concentration,15 QTLs controlling root-shoot Cd translocation factor,and 2 QTLs controlling Cd accumulation in whole plant.Among the detected QTLs,there were 11 QTLs controlling the Cd concentration in shoot and 2 QTLs controlling Cd translocation factor from root to shoot whose phenotypic contribution rate was more than 10.00%,and the phenotypic contribution rate of other QTLs was less than10.00%.The interval of QTL q BRCd C-1-1 and q BRCd C-1-2,controlling Cd concentration in brown rice on chromosome 1,and QTL q RSCd TF-1 controlling Cd translocation factor from root to shoot,are highly coincident,indicating that the coincident interval is involved in controlling Cd translocation factor from root to shoot and Cd concentration of brown rice.There was also overlapping region located on chromosome 7 controlling root Cd concentration（q RCd C-7）,shoot Cd concentration（q SCd C-7）,and brown rice Cd concentration（q BRCd C-7）,indicating that the overlap regions collectively controlled Cd concentration in root,shoot and brown rice.（4）Under Cd stress,there was a significant positive correlation between Cd and Mn concentration in brown rice,also between Cd and Fe,Mn,Cu and Zn accumulation in whole plant.Cd translocation factor from root to shoot was positively correlated with Cu and Zn translocation factor from root to shoot.A total of 38 QTLs related to accumulation of trace metal elements were detected,which could explain 5.20%～17.50%of the phenotypic variation.There were 8 QTLs whose phenotypic contribution rate was greater than 10.00%.There were some overlapped interval compared with Cd related loci.The intervals of QTL q BRCd C-4 controlling Cd concentration in brown rice and QTL q BRZn C-4 controlling Zn concentration in brown rice had overlap regions.There was an overlapped region between QTL q Cd A-4 controlling Cd accumulation in whole plant and QTL q Cu A-4 controlling Cu accumulation in whole plant.By QTL mapping of Cd accumulation related traits in rice,a stable QTL for controlling Cd concentration in brown rice was obtained on Chromosome 1,which contained a key gene for controlling Cd accumulation in D62B brown rice.Through correlation analysis with trace metal accumulation,Cd accumulation in this population may be related to Cu and Zn accumulation.