QTL Mapping Of Tassel Related Traits In Maize (Zea Mays L.)

Male inflorescence,i.e.tassel,is an important organ of maize plant,and presents complex influence to yield permormance of maize varieties.It was reported that sutable tassel architecture,including fewer tassel branch number?TBN?,played as necessary component for higher kernel yield and better kernel quality.Tassel related traits,i.e.TBN,and central tassel branch length?cTBL?are the base of tassel architecture,considered by both scientific researchers and breeders world-widely.In the previous work,a distinct line,EHel?extremely low Ear Height?was derived from the cross of Dan299 and a Pioneer hybrid.EHel possesses a very low ratio of ear height to plant height?<30%?,extremely low than the general maize inbred lines?40%⁴5%?.In order to dissect the tassel characteristics,a segregating populations of F₂ and F_2:3 derived from EHel×B73 was constructed in the present study.We phenotyped?mainly focused on cTBL and TBN?parental lines of EHel and B73,F₂,and F_2:3,and genotyped both parental lines and F₂ via chipset consisted of¹0000 SNPs.Polymorphic SNPs between EHel and B73 were screened out to construct the linkage map.QTL for cTBL and TBN were detected,and 1 genes annotated within the detected QTL confidence intervals of TBN were selected for relative expression level analysi via real-time quantitative PCR?QPCR?.The main results are as follows:1.Phenotypic characterization of cTBL and TBN between EHel and B73The results of phenotype characterization showed that cTBL of EHel presented as29.14cm and 29.21cm in the corresponding years of 2018 and 2019,and no statistical differences were ovserved between years?P=0.96?.The same trend was observed at the performance of TBN?P=0.95?.For B73,statistical differences were detected for both cTBL?P=0.02?and TBN?P=0.0001?between 2018 and 2019.Between two parental lines,the performance of cTBL and TBN of EHel correspondingly exhibited 21%and18%higher than those of B73 in 2018,while no statistical diffenreces were detected?P value was 0.16 and 0.24,espectively?.In the year 2019,non-significance was ovserved at the performance of cTBL between EHel and B73?P=0.10?,while the TBN of EHel was extremely lower than that of B73?P=0.0004?.2.Linkage map constructionThe whole genomes of EHel and B73 parents and F₂ plants were scanned by 10K microarray,and the genotypes of EHel,B73 and F₂ plants were obtained by screening polymorphic SNP.The results showed that a total of 2108 SNP markers showed stable polymorphism.According to the genotypic data of parents and F₂ population,combined with the field phenotypic data of F_2:3 population,a linkage map was constructed.Among the 10 chromosomes?linkage group?of the linkage map,there were more SNP on chromosomes 1?Chr1?,2,3,4 and 8,while less than 200 SNP were distributed on the remaining 5 chromosomes.The total length of the linkage map was 3367.02 cM,and the average distance between markers was 1.60 cM.The map distance of Chr3 is the longest?the map distance of 591.48 cM?,Chr10 is the shortest?176.25 cM?.Among the 10 chromosomes,the average marker spacing of Chr1?1.10 cM?,Chr2?1.21 cM?,Chr4?1.16 cM?,Chr6?1.29 cM?,Chr8?1.49 cM?and Chr10?1.12 cM?was lower than the overall average,while the average marker spacing of the other four chromosomes was higher than that of the whole,and the average marker spacing of Chr9 was the largest?2.60 cM?.3.QTL detection for cTBL and TBN11 QTL were detected for both cTBL and TBN.These QTL distributed on 8chromosomes except Chr1,Chr6.Among these 11 QTL,5 controlled TBN,and the rest 6 controlled cTBL.5 QTL for TBN distributed on 4 chromosomes of Chr1?qTBN1?,Chr4?qTBN4?,Chr5?qTBN5-1,qTBN5-2?,and Chr8?qTBN8?.the PVE of these 5 QTL ranged from 1.04%?qTBN8?to 2.24%?qTBN1,qTBN4,qTBN5-1?.Considering the gene action of these QTL,qTBN4,qTBN8 exhibited as dominance?D?,and the positive allele?increasing the phenotypic performance of TBN?of this QTL is from pollen line of B73.The synergistic allele of qTBN5-1 was additive?A?,from the male parent B73,and the other two alleles were overdominant?OD?,in which the synergistic allele of qTBN5-2 also came from the male parent B73,while the synergistic allele of qTBN1 came from the female parent EHel.A total of 6 QTL,were detected by cTBL on chromosomes 3,5,7,9 and 10.The PVE of the 11 QTL to cTBL is between 3.24%?qcTBL10-1?and 6.26%?qcTBL9?.From the mode of action of these six QTL on cTBL,qcTBL3 showing partial dominant?PD?,and its synergistic allele comes from female parent EHel;qcTBL7showing additive?A?,and its synergistic allele also comes from female parent EHel;The other four alleles showed overdominant?OD?,in which the synergistic alleles of qcTBL5,qcTBL9 and B73 came from the male parent B73,while the alleles of qcTBL10-1 and qcTBL10-2 came from the female parent EHel.4.Gathering characteristics of detected QTLOn Chr5,qTBN5-2and qcTBL5 shared the same flankering SNPs.This gathering characteristics of these QTL suggested that there might present some chromosomal regions or positions controlling the development and performance of both cTBL and TBN on Chr5.Besides,2 detected QTL for TBN on Chr5?TBN5-1 to TBN5-2?exhibited neighboring,i.e.the right flankering SNP of the former QTL served as the left border of the next QTL,and all these 2 QTL formed a continuous chromosomal region.The gathering characteristics suggest that the candidate genes for cTBL might present at wide possible regions of these chromosomes.5.Relative expression level alalysis of selected candidate genesOne annotated gene Zm0000d012741?located in the interval of qTBN8?was screened from 7 QTL mapped to TBN traits,and fluorescence quantitative analysis was carried out.The results showed that the relative expression of this gene in the leaves of EHel and B73 was lower?<3?,and the expression of Zm0000d012741 in root,Internode and male ear of B73 was also lower?<2.5?.From the expression level of this gene in the same tissues of EHel and B73,the expression of Zm0000d012741 in EHel leaves?0.63?was lower than that of B73?1.02?.The expression of this gene in three tissues of EHel was higher than that of B73.Moreover,the expression level of this gene in the male ear of EHel was significantly higher than that of B73,and the expression level of this gene in the male ear of EHel was more than 5 times that of B73.The results of quantitative analysis show that this gene may play an important role in regulating the expression of TBN in maize.