Dissecting Genetic Architecture Of Ear Traits And Studying Mechanisms Of ZmGHT1 Conferring Glufosinate Herbicide Tolerance In Maize(Zea Mays L.)

Germplasms contain the gene resources confering beneficial traits to a species,such as high yield,superior quality,and disease/stress resistance,and it is the basis of crop improvement.As farmers prefer high density during cultivation,ear development has been important restricting factors for maize production,but the molecular and genetic mechanisms of ear number remain unclear.In addition,weed interference is one of major biotic stresses that cause dramatic maize yield losses,with the appearance of herbicide-resistant weeds and the increasing labor cost,it is urgent to screen and create new herbicide-tolerance germplasm.Accurate phenotyping of the germplasm resources was performed,genome-wide association studies(GWAS)and transcriptome sequencing were used to analyze the genetic and molecular mechanisms of ear number trait in maize.The glufosinate herbicide tolerance line was identified by chemical treatment,and the glufosinate herbicide tolerance gene ZmGHT1 in maize was fine mapped,physiological and biochemical mechanism of ZmGHT1 were also analyzed.The main results of this study are as follows:1.The ear number trait was precisely phenotyped in the association panel containg 1223 maize inbred lines in ten environments.After genome resequencing,6.84 million high-quality SNP in associated populations were obtained,and a total of 2286 significantly correlated SNP were identified by GWAS using EMMAX model and FarmCPU models.Twelve environmentally stable QTL were further extracted,with seven QTL have not been found known genes regulating ear development.2.Transcriptome analysis uncovered 1099 and 1737 differentially expressed genes(DEGs)in earless and multi-ear materials,respectively.Specific enrichment of GO terms and KEGG pathways were also identified,indicating the molecular mechanisms regulating the ear number are different for both materials.Haplotype analysis showed that the significant SNP were mainly distributed in the introns or upstream regulatory regions of the candidate genes,and the materials with dominant haplotypes tend to have two ears.3.The QTL mapping population was constructed using the earless and other types of materials as parents.Combined with BSA analysis and molecular marker genotyping of the F2 segregation population,qEN3-3,which was also detected by GWAS,was identified as the major QTL.qEN3-3 was mapped in an interval of 1.44 Mb,the additive effect was 1.31,and explained 46.70%phenotypic variation.Zm00001eb148610 encoding a serine/threonine protein kinase was deduced to be the candidate gene.4.854 maize inbreed lines were screened by spraying 1 g/L glufosinate,and the resistant line L336R was identified.Genetic analysis showed that the resistance was regulated by a single locus,which designated as ZmGHT1.By fine mapping,ZmGHT1 was located in a 2.16 Mb region on chromosome 8,but the recombination was obveriouly inhibited.By comparative genomic analysis,a large number of structural variants(SVs)were identifed between the two reference genomes which resemble the parents used for contructing the mapping population respectively.It’s suspected that similar SVs should be existed between the two parents which inhibited recombination.5.Based on the gene expression analysis and functional annotation,it is deduced that Zm00001eb361930 encoding a transaminase gene is the most likely candidate gene.After glufosinate treatment,lower level of ammonia content and higher activity of GS in L336R were detected compared with those of wild type,suggesting the target gene may participate in ammonia elimination involving GS activity.Taken together,through screening the germplasm resources and combining with genetic,transcriptomic,physiological and biochemical methods,we studied the genetic and molecular regulatary mechanisms of ear number in maize,identified a new maize germplasm resistant to glufosinate,and revealed the physiological and biochemical mechanism of ZmGHT1.This study can provide genetic resources and theoretical support for breeding new maize varieties with high yield potential and herbicide resistance.