GWAS Analysis On The Number Of Vessels In Metaxylem Of Aerial Roots In Maize

As one of the three major food crops,the maize output has exceeded that of rice and wheat at the beginning of 21st century,and it has become the top of the three food crops.During the maize growing process,many factors results in a reduction in yield,among which drought stress is one of the important environmental factors that lead to a reduction in maize production.This abiotic stress will greatly restrict the agricultural and animal husbandry production in most areas.It will also have a serious impact on food production and economic development.During its growth and development process,the maize demands for water far greater than the demand for other substances.In maize plants,the organ responsible for absorbing water is the root system,and the root system as the absorption organ in the plant has a very significant role in maintaining the life,nutrient absorption,and plant growing.However,in the root system,the root metaxylem is mainly responsible for transporting water and nutrients,and in the metaxylem,it is the tubular structure that is directly responsible for transporting water and nutrients inside the plant.So the number of metaxylem vessels is a factor that directly affects the transport capacity of aerial roots in a plant.Therefore,the number of vessels in metaxylem is closely related to transporting plant water and nutrients and responding to drought stress.This experiment uses 508 maize inbred line related groups collected from worldwide as genetic material,and two replicates are planted in three environments:Hainan,Jilin,and Liaoning.Through the genomic association analysis（GWAS）,the genetic basis of quantitative traits in the metaxylem of maize aerial roots are analyzed.The main findings are as follows:1.Correlative analysis of the number of vessels in the metaxylem of maize aerial roots:The investigated target traits show a clear continuous distribution trend and a normal distribution with a broad heritability of 39%,showing a moderate level.There is no significant difference in the average number of metaxylem vessels at the four experimental points in the inbred line,which is around 36.9.There is a correlation between the number of aerial root metaxylem vessels and best unbiased linear predicted values calculated from the data of the four experimental plot.There is a significant difference in the genotype variance of the vessels number in the metaxylem vessels of aerial roots.The variance of the environment and the interaction between the genotype and the environment all show significant differences.However,the interaction between genotype and environment only accounts for a small part of the total variation.2.GWAS analysis of the number of vessels in the metaxylem of the maize aerial roots:The genome-wide association analysis is performed by the MLM model.When the threshold value is P<1.04x10^-5,a total of 17 significant independent SNPs are detected.These17 significant independent SNPs are located on chromosomes 1,2,3,4,6,and 10,respectively,there were 3,4,1,2,6,and 1 SNPs in the confidence interval for each SNP.There are 55 candidate genes in the SNP confidence interval,and the homologous genes in Arabidopsis are used as candidate gene function annotations.The candidate genes with known functions are divided into eight functional types,including signal transduction pathways,transcriptional regulatory pathways,cellular transport pathways,metabolism pathways,secretory transport pathways,RNA editing pathways and oxidation-reduction reactions,and some candidate genes have no functional annotation.A portion of the candidate genes are highly expressed in root and vascular tissues.Furthermore,seven candidate genes related to the number of metaxylem vessels in the maize aerial roots are selected through functional annotation.These seven candidate gene regulatory pathways can be divided into two major categories:transcriptional regulatory pathways and signal transduction pathways.There are five candidate genes in the transcriptional regulatory pathway:GRMZM2G031200,GRMZM2G030710,GRMZM2G422670,GRMZM2G470422,and GRMZM2G123029.The signal transduction pathway class has two candidate genes,which are respectively GRMZM2G007914 and GRMZM2G128315.