QTL Mapping Of Nitrogen Efficient Use Traits In Common Wheat And Relative Species

Nitrogen?N?,an essential plant nutrient,is vital for crop growth and development,including seed germination,root architecture regulation,shoot development,flowering,and grain production.To increase production without further damage to the environment,high-yield crop varieties tolerant of nitrogen deficiencies,or those that can efficiently uptake and use limited nitrogen,are desirable.In this study,we screened efficient nitrogen utilization traits of Aegilops tauschii,and several high efficient nitrogen utilization varieties were characterized.By QTL mapping,closely linked makers were developed based on favorable QTL/alleles identified and were employed into selection of Aegilops tauschii-common wheat introgression lines.Gene involved in nitrogen-deficiency tolerance were characterized through RNA-seq analysis.At the same time,we conducted QTL mapping analysis for nitrogen efficient utilization traits using NAM population,favorable QTL were identified.The contents in this study are as follows:1.The results of hydroponics experiment showed abundant genetic diversityof nitrogen efficienct utilization among 127 Aegilops tauschii varieties.We screened 16 high nitrogen use efficieny and nitrogen-defficiency tolorence vatrieties,18 high nitrogen use efficiencyvarieties and 18 low nitrogen use efficieny and nitrogen-defficiency tolorence vatrieties.Jing Y225 perform well under both high and low nitrogen condition.2.A doubled haploid?DH?population was developed via the cross of Langdon?LDN?and F₁ derived from high nitrogen use efficieny variety Jing Y225 and low nitrogen use efficieny variety Jing Y176.Finally,11 QTLs related to nitrogen uptake efficiency?NUE?,total nitrogen content?TN?,biomass?BM?,yield?GY?and effective tillers?ET?,were detected,on chromosome 1D,2D,3D and 4D chromosome.Five QTLs flanked by Xcfd35-Xgpw4074 on 3D chromosome rigion could be repeatedly detected with the additive effect originated from Jing Y225,indicating that the chromosome region was very important.3.QTL analysis of nitrogen efficient use traits by Drum wheat-Ae.Tauschii DH population showed that,3D chromosome region flanked by Xcfd35-Xgpw4074 contain important gene affecting nitrogen efficient use traits.We use 3 designed SSR marker and 5 public SSR marker in this chromosome region to screen the introgression lines of Jing Y225-Jimai 22,and 13 excellent lines were selected.The selected introgression lines showed higher nitrogen use efficiency,biomass,grain yield,tillering and protein content.Meanwhile,we cross LDN with Jing Y225,and obtained LDN-Jing Y225 double haploid lines.LDN-Jing Y225performed higher efficiency of nitrogen utilization than Langdon.4.Jing Y225 was treated under high and low nitrogen supply condition,and used for transcriptome sequencing.860 differentially expressed genes were detected,in which 680were up-regulated and 183 were down-regulated.Tanscription fators were strongly induced,implying that they may play important role in nitrogen-defficiency response.The differential expressed genes?DEGs?were enriched to 46 biological process in GO analysis,426 DEGs were enriched on to 80 metabolism pathway.We verified 6 important genes,NRT1.1?TraesCS7D01G119800?,IAA15?TraesCS3D01G123400?,LBD37?TraesCS2D01G193400?,SAUR36?TraesCS2D01G383200?,NIR?TraesCS6D01G313100?and NLP3?TraesCS3D01G166900?by qRT-PCR assay,the expression partterns of six genes were consistent with the transcriptome results.IAA15 regulates root growth and development,the expression level was high.The IAA15 genes from 127 Aegilops tauschii varieties were cloned,and sequence alignment analysis showed that,three haplotype of IAA15 present in Aegilops tauschii.The association analysis showed that IAA15 was significantly related to nitrogen-defficiency tolerance.For genetic improvement consideration,we developed a molecular marker,which can be used for IAA15 selection in Aegilops tauschii.5.A nested association mapping?NAM?population,derived from Yanzhan 1?Chinese domesticated cultivar?crossed with HUSSAR?British domesticated cultivar?and other three semi-wild wheat varieties including Cayazheda 29?T.aestivum ssp.tibetanum Shao?,Yunnan?T.aestivum ssp.yunnanense King?and Yutian?T.aestivum.petropavloski Udats et Migusch?,was employed to detect QTLs for nitrogen utilization at seedling stage.An integrated genetic map with 2,059 SNP markers from a 90K SNP chip was constructed.A total of 67 QTLs for RDW?root dry weight?,SDW?shoot dry weight?,TDW?total dry weight?and RSDW?root to shoot ratio?were identified under normal nitrogen condition?N⁺?and nitrogen deficient condition?N^-?.23 favorable QTLs were found to be donated by the domesticated cultivar of Yanzhan 1,in which 15 were detected at N⁺condition and only 4detected at N^-condition.In contrast,the semi-wild cultivars contributed more favorable N^-specific QTLs?8 from CY;9 from YN?,which might be further explored for wheat breeding in adaption to N deficiency.Especially,QRSDW-5A.1 from YN is suggested to be studied by high-resolution mapping.