| Rapeseed(Brassica napus L.)is one of the most important oil crops in China.Seed number per pod,pod numbers and seed weight are the three direct yield components.Additionally,seed weight plays a crucial role in the formation of yield per plant.Therefore,the research and analysis into seed weight is of great significance for improving the yield.In this study,the molecular and cellular studies for seed weight pod length and were conducted,QTL mapping and candidate genes screening were described at the molecular level,paraffin method was used to interpret the variation of seed weight at the cellular level.In our previous study,17 QTLs for seed weight and 18 QTLs for pod length were identified in F2/F2:3/F2:4 populations.After meta-analysis and integration the QTL of seed weight and pod length,the regions of qSWPL.A9-1 and qSWPL.A9-3 were located on A09 linkage group,which regulated seed weight and pod length simultaneously and the confidence intervals were 5.3cM and 13.2 cM.A major QTL,qSWPL.A9-1,can be detected in four environments.It explained 20.1%and 19.0%phenotypic variation of seed weight and pod length,respectively,considering as a pleiotropic major QTL.In this experiment,a near isogenic lines was derived from two parents ZS11(the recurrent parent)and No.73290 at qSWPL.A9-1.Then the major QTL was narrow down and the phenotype were measured in 2013 and 2014.Furthermore,cytological analyses for the parent ZSI1 and NIL plants were conducted.The main results are as follows:1.Construction of near-isogenic linesIn this study,ZS11 and No.73290 were the parents materials,and ZS11 was the recurrent parent.After the crossing between the two parents,we got F1,then backcrossing with ZSI1 consecutively to obtain BC1F1,BC2F1,BC3F1,BC4F1 populations Selecting heterozygous target area and the higher backcross rate by marker-assisted.We got BC4F2 after the self-crossing of BC4F1.2.Genotyping analysisIn 2013 and 2014,we added markers in the primary qSWPL.A9-1 region,and constructed successfully NIL population.Finally,the major QTL was narrowed down between between the mark qBrSF*-2389 and BrSF*-101.There was a significant difference between NIL and ZS11 in the pod length and seed weight(P<0.01).Therefore,the target region was confirmed between BrSF*-101 and qBrSF*-2389 with 140kb.3.Analysis of phenotypic traits By analyzing NIL phenotype in 2013 and 2014 at Wuhan,the pod length of ZS11 was 83.83 ± 6.72 mm and 85.34 ± 6.31mm,significantly higher than the NIL(64.48±7.52mm and 62.65 ± 11.19mm)(P<0.01).The seed weight of ZS11 was 4.37 ±0.29g and 4.99 ± 0.36g,significantly higher than the NIL(3.53 ± 0.58g and 3.99 ± 0.64g)(P<0.01).4.Screening of recombinant plantIn early 2013,we got nearly 200 plants,which were heterozygous and higher backgcrossing rate in target area.At the end of September in 2013,all heterozygous BC4F2 seeds were planted in Wuhan.We obtained 14,000 plants of BC4F3 fine mapping population after selfcrossing of BC4F2,1393 target QTL region exchange plants were filtered by molecular markers,screened recombinant plants can be used for mark encryption and subsequent progeny test.5.The screening of candidate genesComparative analysis was conducted in the area of the results of 140kb interval by bioinformatics,the results showed that a total of 31 candidate genes within the target area 140kb.Gene function has been verified in the majority of this 31 candidate genes,as well as a small number of genes of unknown function,so it is necessary to further fine mapping to identified these 31 candidate genes.6.Cytological MechanismCytological analysis for the parent ZS11 and NIL plants was conducted to study the mechanism of variation into pod length and seed weight.Then,the different of cell size and cell numbers were the main reason for the variance of pod length and seed weight. |
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