Association Analysis Of Ear Traits Under Different Water Treatments In Maize

Maize(Zea mays L.)is the major food crop in China and plays a significant role in ensuring national food security.Drought stress is an important factor limiting maize yield,so the cultivation of drought-resistant maize varieties is an important issue for increasing maize production.In this study,two sets of associated populations(AM173 and AM109)were formed using different types of maize inbred lines as experimental materials.The ear length(EL),ear diameter(ED),ear row number(ERN)and kernel number per row(KNR)of different ear traits were investigated under different water treatment conditions in Yulin of Shaanxi,Yinchuan of Ningxia,Zhangye of Gansu,Urumqi of Xinjiang and Taiyuan of Shanxi in 2020 and 2021.Combining with high throughout SNPs,candidate genes that respond to drought were screened and identified based on genome-wide association analysis.The main research results are as follows:1.The coefficient of variation showed there were widely variant in the AM173 and AM109 populations with(7.73%-27.38%),indicating large phenotypic variation in this population.Meanwhile,the heritability under drought stress of the same trait was lower than that under normal irrigation,indicating that drought stress increased the environmental effect and reduced the genotype effect,thus decreasing heritability.2.Make use of 34,492 high-quality SNP markers obtained from high-throughput molecular marker Maize 6H-60 K chip,the population structure and kinship of all the experiment materials were analyzed in this study,which divided into 11 subgroups.Meanwhile,the kinship results showed that the individuals were far related,which indicatd the population is rich in genetic variation.3.By conducting genome-wide association analysis with the best linear unbiased estimator(BLUE)of the four ear traits,5,4,5,2 assocaited SNPs for EL,ED,ERN and KNR were detected under normal irrigation with 0.26% to 13.01% phenotypic variation explaination.Also,10,19,4,5 associated SNP were identified,explaining 0.04% to 6.45%phenotypic variation explaination.Furthermore,two of them were detected under both water treatments,and 35 specific sites were sepecially detected under drought stress.4.By screening the candidate gene screening,58 candidate genes with expression in spike were obtained.Among them,the candidate genes idenftified under irrigation conditions were mainly enriched in the biosynthesis process of aromatic amino acids(GO:0009073),nitrogen compound metabolism process(GO:0006807),chloroplast RNA processing(GO:0031425)and other biological processes.The candidate genes under drought stress were mainly enriched in biological processes such as carbohydrate transport(GO:0008643),glucose transport(GO:0015758),and disaccharide metabolism(GO:0005984).This indicates that the regulation mechanism of ear development is different under different water treatments.5.Using the public expression data of ear tissues under two different water treatments,17 candidate genes including GRMZM2G118250(LBD6)were screened,and the protein interaction network analysis of them was conducted,which showed these candidate genes mainly play a role in plant growth,development,environmental stress and immune response.In summary,this study conducted phenotype analysis and GWAS using maize association populations under two water treatment conditions,and detected a series of associated SNPs.Through functional annotation of candidate genes within the confidence intervals of these SNPs,several genes related to maize drought stress response,such as GRMZM2G118250(LBD6),were identified,laying a foundation for further exploration of maize drought response from the perspective of ear traits.