Genetic Analysis Of Root Traits In Maize Seedlings Under Low Nitrogen Stress

Nitrogen is an essential mineral element for plant growth and development,which directly affects crop yield.Environmental pollution caused by excessive fertilization is becoming a serious problem in agriculture.Therefore,it is an important scientific issue to improve crop nitrogen use efficiency and increase maize yield under the premise of reducing fertilizer input.The root system is an important organ for plants to absorb nitrogen.Plant roots are highly malleable and can optimize their root structure in different environments to maximize the uptake of nutrients and water from soil.Therefore,genetic improvement of root traits is very important to improve nitrogen use efficiency.In order to analyze the genetic mechanism of maize root response to low nitrogen stress,we used 213 maize inbred lines as materials,combined with genome-wide association analysis,transcriptome data and candidate gene association analysis,screened key genes of maize root response to low nitrogen stress,and mined excellent alleles.The main results are as follows:1.Phenotypic analysis was carried out on 28 seedling traits of 213 inbred lines under normal and low nitrogen conditions.There were abundant phenotypic variations in each trait.The analysis of variance showed that the variety,treatment and the interaction between varieties and treatments of most of the characters reached extremely significant level.The traits and their plasticity of 28 maize seedlings under normal and low nitrogen conditions were analyzed by GWAS using mixed linear model.A total of 261 significant SNPS were identified by association analysis,including 58 SNPS under normal conditions,107 SNPS under low nitrogen conditions,and 96 SNPS under trait plasticity.Under low nitrogen conditions,15 single factor polypotency SNPS were located on chromosome 2,which were significantly associated with total root length,total root length,total root surface area and lateral root length of main radicle.The results of association analysis were annotated,and a total of 230 genes were annotated within 50KB above and below the significant SNP loci.2.B73 was used as test material,normal treatment and low nitrogen treatment were set,and maize roots were sequenced at 1 day（S1）,2 days（S2）and 3 days（S3）.Combined with genome-wide association analysis and differential expression analysis,38 candidate genes were screened.GRMZM2G081930 encoded a NAC transcription factor,which was significantly associated with total root length,total root length,total root surface area and lateral root length of primary radicle under low nitrogen conditions in genome-wide association analysis.The expression level of this gene was significantly different in S0_LN vs S1_LN,S1_LN vs S2_LN,S2_LN vs S3_LN and S2_CK vs S2_LN.The gene was identified as a key candidate gene in this study.3.GRMZM2G081930 was re-sequenced from 213 maize inbred lines.The sequencing length was 5657bp,including 1621 bp upstream promoter region,3478bp coding region and 558 bp downstream region.A total of 591 sequence variations were detected,including 408 SNPS and 183 Indel.Association analysis of candidate genes for seedling phenotypic traits revealed that 50 loci were associated with PRLL_LN,PRL005_LN,PRSA LN and TPRL_LN,including 38 SNPS and 12 Indel.These significant loci divided 213 inbreeding lines into two major haplotypes.There were significant differences in root phenotypes between the two haplotypes.