| Nitrogen is one of the essential nutrients for plant growth and the largest fertilizer input in the agricultural system.Besides developing new fertilizer and improving field management,enhancing plant nitrogen use efficiency is one of the most powerful ways to reduce agricultural input and N surplus in the environment.Compared to other species,oilseed rape(Brassica napus L.)has higher N uptake capacity but poor capacity of utilizing N to produce seed yield(nitrogen utilization efficiency,NUtE).Comparing natural variety in oilseed rape genotypes to identify critical underlying traits of NUtE plays an important role in improving oilseed rape NUtE.This study employed oilseed rape genotypes to select traits closely related to NUtE and evaluate the relative contribution of late N uptake and N remobilization to genotypic variation in NUtE.Leaf transcriptional analysis between oilseed rape genotypes with extremely NUtE was also used to identify the reasons of differential NUtE between genotypes.Target deep sequencing of known genes contributed to NUtE in other plant species was employed to identify hopeful candidate genes which significantly associated with NUtE among oilseed rape genotypes.The main results were listed as below.(1)Nitrogen harvest index,harvest index and seeds number per silique were underlying traits of NUtE in oilseed rape under both pot and field conditions.50 oilseed rape genotypes were grown under high N supplies and low N supplies in both pot and field experiments.The correlations between NUtE and biomass distribution,N distribution,yield components and morphological traits were calculated.Under both the pot and field experiments,at both low and high N supplies N harvest index(the ratio of seed N accumulation to plant N uptake),harvest index(the ratio of seed yield to plant biomass)and seeds number per pod were always significantly and positively correlated with NUtE.Five N-responders,six N-nonreponders,four N-efficient genotypes,and four N-inefficient genotypes were selected from the genotypes performing stably at both the pot experiment and the field trial.Under high N supplies the N-responders had significantly higher N harvest index,harvest index and seeds per silique than the N-nonresponders at both the pot and field experiments.Under low N supplies the N-efficient genotypes also had significantly higher N harvest index,harvest index and seeds number per silique than the N-inefficient genotypes.Two-years pot experiment was conducted to further select the genotypes performed stably.Under both high and low N supplies the genotype zheyou18 always had significantly higher NUtE than Sollux at all experiments.(2)N uptake at the reproductive stage contributed to genotypic variation in N harvest index and stay-green phenotype of genotypes with high NUtE may contribute to its high N uptake during the reproductive stage.Three N-responders,three N-nonresponders,three N-efficient,and three N-inefficient oilseed rape genotypes were further selected based on the similar flowering time.Late N uptake and N remobilization were determined among these genotypes.The cultivar ranks in apparent leaf and stem N remobilization efficiency and amounts of leaf and stem N remobilization were not similar to that of NUtE while the N-reponders had significantly higher root N uptake during the reproductive stage than the N-nonresponders under high N supplies and under low N supplies the genotypes preforming high NUtE also had significantly higher late N uptake than these performing low NUtE.The time courses of plant biomass and N change between N-efficient genotype Zheyou18 and N-inefficient genotype Sollux during the reproductive stage were determined.50 days after flowering,Zheyou18 had significantly higher green leaf N concentration and higher pod biomass.At the similar stage,Zheyou18 had significantly higher N uptake capacity than Sollux while before flowering no significant plant N uptake differences were found between them.Transcriptionally comparing between young and old leaves between Zheyou18 and Sollux found the old leaf of N-inefficient genotype Sollux senesced early than that of the N-efficient Zheyou18.The genes related to photosynthesis and carbon metabolism were abundant in the old leaf of zheyou18 which suggested that the shoot of zheyou18 may provide more energy to maintain the capacity of root N uptake during the reproductive stage.(3)SNPs in NPF8.3 gene significantly associated with genotypic variation in nitrogen efficiency in oilseed rape.Seedling leaf nitrate concentration of 84 oilseed rape genotypes,and seed yield at both high and low N supplies of 28 oilseed rape genotypes in the same field experiment were found from other researches.Glutamine synthesis(GS)NAC(NAM,ATAF1,and CUC2)transcription factor family,NPF5(NRT1 / PTR family),NPF8 and SMG7(Suppressor with Morphogenetic effects on Genitalia 7),known genes contributed to nitrogen efficiency in other plant species,were used to conduct target deep resequencing among 84 oilseed rape cultivars to find SNPs significantly associated with genotypic variation in nitrogen efficiency.SNPs causing amino acid change were found.Three SNPs of NPF8.3gene Bna A09g56930D significantly associated with seed yield at high N supply.One SNP of NPF8.3 gene Bna A06g09430D,three SNPs of Bna A09g56930D,seven SNPs of BnaC08g39460D were found associated with seed yield at low N supply.One SNP of NPF5 gene BnaC03g22680D and eight SNPs of BnaC04g47170D were significantly associated with seed yield at low N supplies.NPF8.3 gene Bna A09g56930D had two SNPs associated with seed yield at both high and low N supply.In conclusion,both nitrogen harvest index and harvest index closely correlated with NUtE in oilseed rape.The genotypic variation in nitrogen harvest index were contributed by N uptake during the reproductive stage other than N remobilization from the vegetative organs.The stay green phenotype of N-efficient genotype may contribute to maintain its high N uptake capacity during the reproductive stage.NPF8.3 gene is a hopeful candidate gene to improve NUtE of oilseed rape. |
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