| Yield and quality are the important target characteristics in wheat breeding.The spike of wheat is closely related to yield and quality.Spike density and processing quality are important traits in modern wheat production and are controlled by multiple gene loci.Here,a mutant S-Cp1-1 with compact spikes was obtained by chemical treatment.The mechanism of mutant spike variant was identified with genetic mapping,slice observation,transcriptome analysis,processing quality measurement,etc.The mechanism of increased spike density and improved processing quality of S-Cp1-1 was primarily analyzed.The main results are listed as follows:1.The Cpl locus,which controlled the spike density in S-Cp1-1,was initially positioned at 5 AL with 90 K SNP array,by using a mapping population derived from S-Cpl1 × br220.Further,using a F2 population and SSR markers,Cp1 was mapped within 1.6 cM genetic distance.By comparing the released Scaffolds and BACs sequences,we found that this region contained the Q gene.Therefore,an STS marker qs1 within Q was designed,and found to be closely linked to compact spike trait in the a F3 population with10,100 individuals.Then we determined that the gene inducing compact spike in S-Cp1-1 is Q.The Q gene site in S-Cp1-1 was sequenced,and a missense mutation was found in the 10th exons,which was the binding region of miRNA172.The mutation did not affect the threedimensional structure of the Q protein.The mutated Q allele in S-Cp1-1 was named as Qc1,and its expression level increased significantly in the early stages of spikes development.The up-regulated expression of Qc1 was due to the mutation interfering the binding between miRNA172 and Q,and ultimately interfered with the transcribed regulation of miRNA172.The effect of Qc1 on spike density was confirmed by analyzing nine independent common wheat mutants possessing four different Qc alleles(Qc1-Qc4).These alleles contained four different point mutations in the miRNA1 72-binding site,supporting a causal relationship between the transcriptional regulation of Q by miRNA172 and the compact phenotype.2.The microscopic comparison of S-Cp1-1 and wild-type spike was analyzed.The longitudinal sections of rachis revealed a decreased size of cells in S-Cp1-1.Transverse sections of rachis revealed that cells of S-Cp1-1 were reduced in size and increased in number,and,notably,the number of vascular bundles in S-Cp1-1 was increased.The parameters reflecting the processing quality of S-Cp1-1 and WT were compared.In contrast to the WT control,grain protein content,wet gluten content,zeleny sedimentation value,and development time were significantly higher in S-Cp1-1.The bread volume made with S-Cp11 flour increased by 37%compared to the wild type.No variation in the composition of gluten was observed between S-Cp1-1 and WT,especially HMW-GS.The effect of Qc1 on processing quality was confirmed by analyzing independent common wheat mutants possessing four different Qc alleles as well.The grain protein content of individual plants belonging to two F2 populations was measured,and we found that Qc1 had a strong positive effect and dose effect on the grain protein content.These results proved that the overexpression of Q was of great value to wheat breeding.3.RNA-Seq analyzed the different expressional genes of young spike between S-Cp11 and wild-type.A total of 1802 differential expression genes were detected,of which 448 genes were upregulated,while 1,354 genes were downregulated.Based on functional annotations and GO analysis,it had been found a plenty of differential expression genes were enriched in the cellular process,catalytic activity and binding.KEGG analysis found that differential expression genes were involved in 103 metabolic pathways.The analysis of nitrogen metabolism and phenylalanine biosynthetic pathways indicated that the key enzymes in both metabolic pathways had significantly changed at the transcription level,which revealed the downstream genes and potential regulatory network of Q. |
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