GWAS Analysis On Genetic Basis Of Brace Root Traits In Maize

Maize is the most important food and feed crop in the world.The increase and stability of maize production directly affects the global food supply security.However,the increase of maize yield is affected by many factors,among which plant lodging is one of the most important factors.Plant lodging can be divided into stalk lodging and root lodging.Therefore,the severity of plant lodging is mainly affected by stalk characteristics and root structure.As an important part of root system,the role of brace rooting in lodging resistance of maize plants has attracted more and more attention.Because of the complex structure of roots,maize traits change with the changes of environment,which makes it difficult to evaluate and study the brace rooting traits.At present,the research on brace rooting mostly focuses on morphology and structure,but in recent years,important progress has been made in molecular markers.The identification of QTL of brace rooting traits from multiple recombinant inbred lines has deepened the understanding of brace rooting in maize.However,these molecular markers often have recombinant population specificity.In order to obtain the molecular markers of common brace root traits in maize plants of different consanguinity,GWAS analysis should be carried out using related populations as materials.Therefore,we used the natural population of maize as material to mine SNP loci and related candidate genes controlling brace rooting traits by Genome-wide association analysis technology,which provided theoretical basis for elucidating the molecular pathways related to brace rooting growth and development and studying the measures to regulate brace rooting growth of maize.In this study,508 inbred lines were planted in Ledong County,Hainan Province,and Shenyang City,Liaoning Province,in 2015 and 2016.The number of brace root tier number,number and the radius of brace root of maize were determined twice in each place.The results of Genome-wide association analysis were performed using the best unbiased linear estimation(BLUP)excluding environmental factors as phenotype values.The main results are as follows:1.Brace root tier number of Genome-wide association analysis: the phenotypic data of brace roots are normal distribution,the generalized heritability calculated by phenotypic data is medium level(0.37).A Genome-wide association analysis of brace root tier number was conducted by using the Farm CPU.The threshold was set at 1.04 x 10-5.Fourteen SNPs were obtained,which were significantly independent of brace root tier number.They were located on chromosomes 1,3,5,6,8,9 and 10,respectively.According to the functional annotations of the candidate genes screened by the SNP,it was inferred that nine genes were related to brace root tier number,mainly involving phytohormones and zinc ion binding.Protein and calcium binding protein.2.The radius of brace root of Genome-wide association analysis: The phenotypic data of the radius of brace roots showed normal distribution,and the general heritability was 0.58.The threshold of Genome-wide association analysis was set at 1.04x10-5.Two SNPs,which were significantly independent of the radius of brace root,were located on chromosomes 1 and 2,respectively.According to the functional annotations of screening candidate genes by SNP,it was inferred that one gene was related to the radius of brace root,mainly related to zinc finger protein.3.Brace root number of Genome-wide association analysis: The phenotypic data of the number of brace roots showed a normal distribution,a broad heritability is 0.45.When the threshold of Genome-wide association analysis was set to 1.04x10-5,no significant independent SNP was obtained,but a single SNP was screened when the minimum P value was 1.139E-05.Two genes were identified based on the SNP.One of the genes GRMZM2G457929 was mainly related to auxin glycosyltransferase.4.The three characteristics of brace rooting are different in different sub-groups.Brace root tier number is larger in tropical and subtropical TST consanguinity.Brace root number and the radius of brace root appear more extreme values in tropical and subtropical TST consanguinity.There are significant correlations between the three characteristics of brace rooting.The correlation between brace root tier number and the radius of brace root is the highest,indicating that in some cases.In tropical and subtropical environments,plants need more brace root tier number,brace root number and the radius of brace root to provide fixation and support for plants.