| Flowering time represents the transition from vegetative growth to reproductive growth in maize.It is not only an important adaptive trait,but also determines the life span and the grain yield.Maize is not only an important food crop,but also an important model crop for heterosis research.It is of great biological significance and application value to analyze the genetic mechanism of heterosis of Maize Flowering time.In this study,flowering time of two hybrids,Zhengdan 958 and Xianyu 335,as well as their parental inbred lines,F2:3 populations,hybrid mimic lines were evaluated in field.Using BSA and transcriptome sequencing techniques,key genes and regulatory networks conferring the flowering time heterosis were analyzed.Moreover,to explore the genetic architecture of flowering time.Main results are as following:1.Flowering time between inbred lines and hybrids were different significantly,and as did in plant height.Similarly,there was significant difference between RIL958 and RIL335 in flowering time.With the increase of inbreeding generations,the flowering time delayed.However,the range of flowering time within early flowering materials and late flowering materials remained unchanged.The delayed flowering time is possible associated with inbreeding depression.2.Zhengdan 958,Pioneer 335,their parents,F2:3 populations and RIL population were used as basic materials.Through the analysis of DNA re-sequencing of early and late flowering mixed pools,there 18 significant QTL intervals in F2:3-335 population,18 significant QTL intervals in F2:3-958 population,17 significant QTL intervals in RIL335 population and 6 significant QTL intervals in RIL958 population were uncovered.Of them,several consistant QTLs were identified.Such as a locus was co-located at a 4.4M interval of Chr.l in F2:3-335 and RIL335;one locus was co-located within a 2.8M interval of Chr.5 in F2:3-958 and F2:3-335;a locus was co-located at a 1.7M range of Chr.1 in RIL958 and RIL335;and two loci were co-located at two 1.9M and 2.9M regions of Chr.10 in F2:3-958 and RIL958.3.During the progress of inbreeding depression,decrease rate of heterozygosity was slower than desired.The recombination rate of different maize materials were stable and related to the change of deleterious alleles.In different groups of plant materials,deleterious SNPs were account for 4.57～4.84%of total,novel SNPs account for 51%.With the inbreed times increasing,the share of deleterious SNPs showed a little decrease,but no change in a certain background.The inbreeding depression is possible related to the accumulation of deleterious alleles.4.Transcriptome analysis showed that the differentially expressed genes within early and late flowering populations were mainly associated with cytoskeleton protein binding,oxygen-containing compound reaction,polysaccharide catabolism,protein auto phosphorylation and response to biological stimulation.The results of gene co-expression network analysis showed that the gene expression of F2:3 mixed pools were highly correlated within the corresponding flowering time group of RILs.The genes in the gene co-expression network were significantly related to the heterosis of plant height,ear height,and ear length.Three key genes,Zm00001d017050,Zm00001d03894 and Zm00001d039255,which may be involved in the regulation of heterosis in flowering time.The transcription factors of WRKY,MYB and ERF family may play an important role in flowering regulatory network.5.The regulation of Heterosis in flowering may be based on the degradation of sucrose as an important signal to regulate genes in the clock regulatory pathway.The possible regulation mechanisms of the heterosis in flowering time were probably as following:(1)to sensor the outside environmental stimulation;(2)the levels of the K+ changing;(3)the signals are transduced into cells transduction of through the K+ channel;(4)the protein kinase are phosphorylated,thereby results in the cell anti-stress reactions;(5)and finally influences the flowering time. |
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