| Zea mays L.is the largest food crop in the world and it is also an important forage source.The cell wall components of maize stalk not only play an important role in the resistance to lodging,but also have profound influence on the palatability and digestibility of forage maize.Therefore,it is of great significance to study the genetic basis of the cell wall components and digestibility of maize for the breed of excellent forage maize.Two RIL?recombinant inbred lines?populations?population I:B73×By804,population II:Zheng58×HD568?and one associatied population contained 368 global maize inbred lines were used in this research.The linkage analysis and the GWAS?genome-wide association study?were applied to analyze the genetic structure of the cell wall components and digestibility of maize stalk,and then provide theoretical basis for forage maize breeding.The main resluts are as follows:1.In order to obtain the phenotype of the cell wall components and digestibility traits,two RIL population were investigated under two environments during six periods.The results indicate that there is a significant correlation between any two investigated traits,which are affected by genetic and environmental effects.At the same time,with the growth of the plants,the average contents of ADF and NDF gradually increased in both populations,the average content of ADL showed a downward trend and the average performance of IVDMD and IVNDFD decreased first and then increased.The average content of CEL in population I showed no any regularity and that of populaion II was decreased at harvest period with no significant variations in the first five periods.2.In population I,a genetic map containing 756 SNP markers with a total length of 1607.71 cM was applied to perform QTL mapping based on the ICIM?Inclusive composite interval mapping?.A total of 72 QTL controlling the cell wall compositions and digestibility of maize stalk were detected in 6stages and distributed on 38 chromosome regions.The QTL controlling ADF,NDF,ADL,CEL content,IVDMD,and IVNDFD were 15,20,11,10,13,and 3,respectively.Each loci contributes a 1.52%to20.01%of the phenotypic variation,and approximately 27.8%of the QTL?20/72?explained>10%of the phenotypic variation,72.2%?52/72?of the QTL explained?10%of the phenotypic variation.These results implied that the cell wall composition and digestibility traits are affected by a few major QTL and a lot of minor effect loci.3.In population II,a genetic linkage map containing 1358 SNP markers and a total length of1985.21 cM was used to perform QTL mapping based on the ICIM.A total of 119 QTL controlling the cell wall compositions and digestibility of maize stalk were detected in 6 stages and distributed on 68chromosome regions.The QTL controlling ADF,NDF,ADL,CEL content,IVDMD,and IVNDFD were17,17,19,16,23,and 27,respectively.Each loci contributes a 1.62%to 18.64%of the phenotypic variation,and approximately 14.3%of the QTL?17/119?explained>10%of the phenotypic variation,85.7%?102/119?of the QTL explained?10%of the phenotypic variation.4.GWAS based on a mixed linear model that considered population structure and genetic relationships was performed for six cell-wall-related traits,the phenotypes of them were investigated in an associated population of 368 maize inbred lines in seven environments and 559285 SNP markers with a minimum allele frequency higher than 0.05 obtained with DNA chip platform and RNA sequencing technology were used in it.A total of 102 and 31 loci that were significantly associated with cell wall components and digestibility were detected at levels of P<1 x 10-4 and RMIP?Resample model inclusion probability??0.1,and each locus explained 4.2%-6.7%of the phenotypic variation.A key enzyme gene in the lignin biosynthesis metabolic pathway,ZmC3H2,was discovered by functional annotation of candidate genes at these loci.Some loci that are significantly associated with the target traits are located on the QTL hotspots regions by comparing the results of association analysis and linkage analysis.5.The results of fluorescence quantitative experiments showed that ZmC3H2 and its homologous gene ZmC3H1 were both expressed in roots,ears,tassels,leaves and stems of maize.The relative expression of the two genes in each tissue was significantly different.At the same time,the gene editing vectors of ZmC3H1 and ZmC3H2 were constructed and the seeds of the transgenic T0 plants that had been successfully edited were obtained. |
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