Genetic Analysis Of Root Morphology Under Different Salt Treatment Conditions In Maize At Seedling Stage

Maize is the largest food crop in China,and it is also an important feed crop and industrial raw material,which plays an important role in ensuring food security and promoting national economic development.Soil salinization is one of the main factors limiting the development of maize production.Root is the main organ to absorb water and nutrients.The root system is the organ directly in contact with the soil.It is the first line of defense for plants to cope with the adverse effects of salt stress.Identifing the key genes for root development and salt tolerance have important theoretical and practical significance for the genetic improvement of maize roots.In this study,319 maize inbred lines were used as materials to study the genetic mechanism of root response to salt stress in maize seedling stage,and the key genes were verified.The major results are as follows:1.A total of 18 seedling traits such as primary root length,total root length,and root dry weight of 319 inbred lines were identified under normal and salt stress conditions.There were extensive phenotypic variation in each trait,and the coefficient of variation was more than 10%,variation ranged from 2.08 fold to 68.92 fold difference;analysis of variance showed that all traits were significantly different between genotypes,treatments and genotypes x treatments.Genome-wide association study using 163,930 high-quality SNP was conducted for 18 traits under normal and salt stress conditions.A total of 192 significant SNPs were detected,79 significant SNPs were detected under the normal condition that could explain 6.01%-22.73%phenotypic variation;and 113 significant SNPs were detected under salt stress conditions that could explain 6.87%-24.17%phenotypic variation.A total of 539 genes were identified within the 100 Kb(50 kb upstream and downstream of the SNP).A SNP associated with the primary root length was mapped on the chromosome 2,and the candidate gene GRMZM2G325131 encodes a protein homologous to the P-subunit of anthranilate synthase in a tryptophan-dependent auxin;a SNP that is significantly associated with root diameter under salt stress was identified on chromosome 1,and the candidate gene GRMZM2G480386 belongs to the YUCCA gene family and functions in tryptophan-dependent IAA biosynthesis.2.The full gene sequence,upstream and downstream regulatory regions of GRMZM2G325131 gene were re-sequenced in 319 maize inbred lines,71 landraces and 32 teosintes.A total of 903 SNPs and 252 Indels were detected for 9204 bp sequence.In the inbred line population,candidate gene association analysis was performed on GRMZM2G325131.A total of 6 variants were detected to be significantly associated with primary root length.The inbred line population can be divided into 4 haplotypes based on 6 significant variants,and primary root length showed significant difference between 4 haplotypes(P=1.1e-07).The gene expression level of GRMZM2G325131 was significantly correlated with primary root length(r=0.65).The haplotype was classified by SNP453 and Indel959.The primary root length and gene expression of haplotype GT were significantly higher than haplotype T-,SNP453 and Inde1959 may be the functional variants of the gene;during the domestication and improvement of maize,the frequency of haplotype GT gradually increased from 28%to 86%.The full-length cDNA sequence of GRMZM2G325131 gene was cloned from maize inbred line B73 and constructed into an overexpression vector.It is currently being transformed in Arabidopsis thaliana and maize,and the over-expressing material will be created to further explore the molecular mechanism of GRMZM2G325131 affecting maize root elongation.3.The full gene sequence,upstream and downstream regulatory regions of GRMZM2G480386 gene were re-sequenced in inbred lines,landraces and teosintes.A total of 578 SNPs and 180 Indels were detected for 5684 bp sequence.In the inbred line population,candidate gene association analysis was performed on GRMZM2G480386.A total of 5 SNPs were detected to be significantly associated with root diameter under salt stress.A total of 3 haplotypes based on 5 significant SNPs were identified,there was a significant difference in root diameter between haplotypes(P=4.6e-04).According to SNP-1998,SNP-1975 and SNP-1919,the diameter of haplotype CCC roots was significantly higher than that of haplotype TTA under salt treatment conditions;SNP1549-G has significantly higher root diameter than SNP1549-C;root diameter SNP2638-T was significantly higher than SNP2638-C.During the domestication and improvement of maize,haplotypes CCC,SNP1549-G and SNP2638-T were positively selected,and the gene frequencies showed a gradual increase.