Analysis Of Rice Germplasm Nitrogen Use Efficiency And The Genetic Basis Of Rice Ionome

Cultivated rice(Oryza sativa L.)is one of the most important crops and it is estimated to feed almost half of the world's human population.'Ionome' was defined as all the mineral nutrient and trace elements found in an organism which play essential roles in growth,development,disease resistance and stress responses.For people who consume rice as staple food,minerals intake via rice account for a large proportion of their mineral nutrition.Improving accumulation of essential elements and reducing potentially toxic elements in rice are thus of fundamental importance for food quality and human health.In addition,rice metabolome,especially for the secondary metabolites,is the most direct embodiment of rice growth and development.It is important to study the genetic basis of rice metabolome for understanding the genetic bases of essential agronomic traits and biochemical regulation mechanism of rice.533 rice collections were selected for this study,the ionome and metabolites were determined by ICP-MS and LC-MS/MS for these collections.Through the genome-wide association study,we got results as follows:1.The nitrogen absorption and utilization display differences between different types of rice collections.Nitrogen could be enriched in the grain of rice.Treatment without nitrogen can stimulate the potential activity of rice to use the nitrogen.High yield varieties present the highest absorption and utilization ability.Indica show higher nitrogen accumulation and nitrogen use efficiency,which may lead to the higher grain yield.We choose the nitrogen accumulation of straw and grain,nitrogen use efficiency for grain(NUEg)and grain yield(GY)for clustering,dividing the 533 collections into 3 categories,including high absorption and utilization with high yield,low absorption but high utilization with high yield as well as low absorption and utilization with low yield.Furthermore,35 extreme collections in these 3 groups were screened out as high nitrogen use efficiency materials for the next research.2.Wide variation was found in ionome of 533 collections among different environments,tissues and subpopulations.The results are as follow:Specific distribution of rice ionome in different tissue:N,P,Cu and Mo show higher enrichment degree in brown rice,which is benefit for the quality of rice.K,Ca,Mg,B,Na,Mn,Fe and Zn in straw of heading period as well as mature straw are higher than that in brown rice,this is benefit for rice photosynthesis and stress-tolerance,and thus the yield is guaranteed.Regardless of the soil environment,the concentration of Al,Co,As,Cd and Pb in straw of heading date as well as mature straw are higher than brown rice,this indicate that rice plants have evolved strategies to limit their accumulation in grains.Specific distribution of rice ionome in different environments:The concentration of Mo in 3 different tissues of these collections which were plant in Hainan(HN)is higher than that in the other treatment.This may cause of the higher concentration of Mo in soil of HN.The concentration of Zn and Cd in brown rice as well as mature straw from Youxian(YX)is higher than other treatments.This may cause of the higher concentration of Cd and Zn in soil of YX.Specific distribution of rice ionome in different subpopulations:Japonica accessions possessed a little higher concentration in almost elements.While Cd in brown rice of japonica was much lower than that of indica.Based on the PCA,we observed that ionome of indica and japonica differed in response to low N condition.The correlations of many elements in cultivated rice showed differences in different tissues and field conditions.For example,the correlations of Zn and Co were observed in shoots and straws of both two fields,while the correlations of Mn and Cd,Mn and Cu were only observed in shoots and straws from normal field.There was also positive correlation observed between HD/Cd.3.GWAS and genetic basis of rice ionomeWe performed GWAS for ionome of different tissues from N90 and NO.Totally,we obtained 850 loci associated with at least one element,inwhich 139 loci were reproducible.Then we seclected OsMOTl,OsCCX2,OsZIP5 and OsGhd7 as the candidates,and the yield result support the assumption for the function of OsGhd7 which control the N and Cd accumulation in Indica.4.GWAS and genetic basis of rice metabolome840 metabolites were determinnated in 493 rice collections,which display a significant difference between indica and japonica.Combining the results of GWAS with the existing metabolites regulation network,we verified 5 unknown genes.Then we identified 166 unknown metabolites according to the result of mGWAS,this indicate that mGWAS can not be only used to identify the function of the unknown genes,but also to identify unknown metabolites.Further analysis mGWAS hotspots,we found there is a significant difference between indica and japonica.Above all of the 514 loci,over 2/3 loci exist significant difference between indica and japonica.And this result reflects more obvious for the loci correlation with the specific metabolites between indica and japonica.