QTL Analysis Of Cadmium Tolerance In Rice Seedlings And Magnesium Accumulation In Rice Grains

Rice is one of the most important food crops in the world,with nearly half of the world's population living on rice as staple food.However,Cadmium?Cd?pollution is serious in farmland soils of some regions in China,leading to excessive Cd in rice grains.Magnesium?Mg?deficiency results in some human diseases,and increasing Mg content in rice grains is one of the strategies to increase human Mg intake.Therefore,it is of great significance to develop new rice varieties with Cd tolerance and high Mg accumulation in grains by identification of QTLs for Cd stress tolerance and Mg content in grains.In this study,a RIL population containing 132lines derived from a cross between 93-11 and PA64s,two rice varieties with significant differences in Cd tolerance and grain Mg content,were used for QTL mapping with high-density genetic map.?1?The Cd stress treatment of rice seedlings was carried out by hydroponics with 50?mol/L Cd Cl₂.The nutrient solution without Cd Cl₂was used as control.The Cd tolerance coefficients of seedling length,root length,shoot dry weight,root dry weight and total dry weight were used as the Cd tolerance indexes.Under Cd stress treatment and control conditions in hangzhou and Lingshui,a total of 36 related QTLs were detected,distributed on chromosomes 1,2,3,4,5,7,9 and 10,with contribution rate ranging from 0.89%to 18.10%.Under the control condition,there were 3 QTLs for root length,3 QTLs for seedling length,3 QTLs for root dry weight,3 QTLs for shoot dry weight,and 3 QTLs for total dry weight.Under the Cd stress,there were 2QTLs for root length,4 QTLs for seedling length,3 QTLs for root dry weight,3QTLs for shoot dry weight and 3 QTLs for total dry weight.In addition,2 QTLs for root length,1 QTL for seedling length,1 QTL for root dry weight,1 QTL for shoot dry weight,and 1 QTL for plant total dry weight tolerance to Cd stress.?2?q CDSL1.1 and q CDSL1.2 were detected in both field traits of Lingshui and Hangzhou under Cd stress.In order to verify whether q CDSL1 plays a role in response to Cd stress,we constructed a chromosome segment substitution line in93-11 background with q CDSL1 from PA64s,CSSL^{q CDSL1}.Under Cd stress,the seedling length of CSSL^{q CDSL1}was significantly increased compared with 93-11.In addition,some QTLs for different traits were mapped in the same or adjacent region of chromosomes,which indicated those traits were controlled by a series of genes or a multi-effect gene.Moreover,these QTLs are reliable and to be further mapped and cloned.?3?A total of 7 Mg content related QTLs were detected in rice grains in Hangzhou and Lingshui,distributed on chromosomes 1,3,4,5,6,8 and 11,respectively,with contribution rate ranging from 8.1%to 21.7%,among which qGMC1.1 and qGMC1.2 were detected in the same region both in Lingshui and Hangzhou,we selected the qGMC1 for further fine mapping.?4?The chromosome segment substitution line in 93-11 background with qGMC1 from PA64s,CSSL^qGMC1was constructed.Compared with the control 93-11,Mg content in grains was increased significantly in CSSL^qGMC1.Then,the CSSL^qGMC1was crossed with 93-11 and self-crossing to obtain the BC₅F₂population,with which we further mapped qGMC1 to a 381 kb region.The study laid the foundation for further cloning of qGMC1.In summary,a total of 36 related QTLs were detected in this study under Cd stress and the control condition,and q CDSL1 was verified to control the responses to Cd stress.Total of 7 QTLs were found to be associated with Mg content in rice grains,and qGMC1 was further mapped in 381 kb region.Therefore,our study provided genetic resources and theoretical basis for development of Cd-resistant and Mg-nutritious rice varieties.