Genome-Wide Association Analysis For Identifying The Genetic Loci And Materials Of Efficient Magnesium Absorption Rice

Magnesium（Mg）is an essential nutrient for plant growth and development.It is an important component of leaf chlorophyll and plays an critical role in photosynthesis and carbohydrate distribution.Currently,the application of chemical fertilizers in China has been increasing continuously,while the application of Mg fertilizer is very few.Meanwhile,both crop multiple cropping index and yield potential of new crop varieties have also been increased,which result in extraction of a large quantity of available Mg from the soil every year without corresponding supplement.The continuous consumption of Mg in the soil leads to the loss of balance of nutrients in the soil.It is estimated that about 54%of the soil in China needs magnesium fertilization in different degrees.Compared with other nutrient elements,the research on Mg nutrition is relatively less.There are few studies on the effects of Mg nutrition on the growth and development,grain yield,quality and physiological metabolism of field crops.The mechanism of absorption,transport,storage and distribution of Mg ions(Mg²⁺)in plants is largely unknown.In this study,207 fully sequenced core germplasms were used as the research materials.In a phytotron,these 207 materials were grown in a hydroponics system at seedling stage.Using the genome wide association study（GWAS）to explore the genetic variation loci related to the absorption and transport of Mg²⁺ in rice.The selected materials with significant difference of Mg²⁺ concentration at the seedling stage were further evaluated in paddy field for statistically analyzing the relationship between some important agronomic traits and the Mg utilization efficiency.The major results were obtained as below:1.Decreasing Mg supply level could significantly reduce the growth of root and shoot,as well as Mg concentration in the plant.The shoot to root biomass ratio was not significantly affected by limited Mg supply,however,Mg deficiency could enhance Mg distribution from root to shoot,thus,increase the ratio of shoot to root Mg content.Although low Mg supply decreased leaf chlorophyll and Mg content,there were no significant relationship between the two parameters.2.In comparison to Indica species,Japonica species commonly showed lower translocation efficiency of Mg from root to shoot,while total Mg accumulation in the plant was higher under low Mg supply.The GWAS was used to analyze the genetic variation of 207 core germplasms for change of absolute and relative shoot Mg concentration,relative proportion of Mg translocation from root to shoot under normal and low Mg supplies.Total 12 quantitative trait loci（QTLs）for Mg efficiency were identified by comparison,which could contribute to 19.31-33.32%of the Mg-deficiency-induced change of shoot Mg content.Similarly,there were total 7 QTLs and 15 QTLs isolated that contributed to 20.04-25.54%and 19.23-33.51%of Mg-deficiency-induced change of the total Mg content and shoot to root Mg ratio in the plant,respectively.Notably,a putative Mg²⁺ transporter gene is located in the region between qSMg11-1/qToMg11-2/qTrMg11-1 of the most prominent QTL for efficient Mg uptake and distribution.3.The materials that showed higher efficient Mg²⁺ uptake and translocation under only normal,only limited or broad range of Mg supplies,respectively,were obtained in the hydroponic screening experiments of 207 core germplasms.Some representative materials were planted in a paddy field.Three of the selected materials（xh28,xh75,xh144）displayed significant higher Mg allocation and biomass in both seedling stage at hydroponic system and field condition,as well as higher final grain yield than other materials.In summary,this study provided important candidate gene resource and potential materials for in-depth identification of the genes and breeding for Mg efficient acquisition and utilization of rice.