Screening And Transcriptome Analysis Of Millet With Low Nitrogen Tolerance Under Low Nitrogen Stress

Nitrogen is one of the most important elements required for plant growth and development.The low absorption and utilization efficiency of crop nitrogen is an important factor limiting the increase of crop yield.Therefore,studying the regulatory mechanism of plant response to nitrogen deficiency has important theoretical significance for cultivating nitrogen-efficient crop varieties.Millet(Setaria italica)has the characteristics of strong resistance to stress,wide adaptability and small genome.With the release of millet genome,millet has become an ideal material for monocotyledonous crops to excavate plant stress tolerance genes and study stress tolerance.This study measured the phenotypes of 45 foxtail millet core germplasms,seedling height(SH),root length(RL),leaf length(LL);leaf width(LW),leaves number(LN),number of roots(NR),fresh weight of root(FWR),fresh weight of shoot(FWS),dry weight of root(DWR),dry weight of shoot(DWS),dry weight of plant(DWP),root-shoot ratio of dry weight(R-S),nitrogen content of shoot(NCS),nitrogen content of root(NCR),nitrogen content of plant(NCP),nitrogen accumulation of shoot(NAS),nitrogen accumulation of root(NAR),nitrogen accumulation of plant(NAP),nitrogen physiology efficiency of shoot(NES),nitrogen physiology efficiency of root(NER),nitrogen physiology efficiency of plant(NEP)under normal nitrogen treatment and low nitrogen treatment,comprehensively evaluated its resistance to low nitrogen stress and selected low nitrogen tolerant cultivars;then selected one low nitrogen tolerant cultivar for transcriptome sequencing,analyzed differentially expressed genes,and clarified its low nitrogen tolerant mechanism.Breeding provides a theoretical basis.The results were as follows:1.Compared with normal nitrogen conditions,foxtail millet seedlings under low nitrogen stress had significantly improvement of root length,root-shoot ratio,number of root,shoot nitrogen physiology efficient,root nitrogen physiology efficient,plant nitrogen physiology efficient,the remaining 17 indicators have significantly reduction.2.The comprehensive low nitrogen tolerance coefficient(X value)method and the comprehensive evaluation D value method based on the membership function are used to dividemillet varieties low nitrogen resistance of into 5 types were classified into Strongly resistance,Resistance,Medium resistant,Sensitive,Highly sensitive.Five varieties with strong low nitrogen tolerance were screened,namely 11,14,17,35 and 39.The main low nitrogen tolerance traits were DWR,FWR,RL,FWS,LN,LW,LL,NAP,NAS,DWP,DWS,NAR,NR,SH,and SPAD.3.The leaves of the low nitrogen-tolerant variety 11 were treated normally and treated with low nitrogen stress,and then the transcriptome was sequenced.2543 differentially expressed genes were identified,of which 1212 genes were significantly up-regulated and 1,331 genes were significantly down-regulated.Significantly enriched in 22 GO functional categories and 8 KEGG metabolic pathways.The differential expression of these genes can be used as a candidate gene for screening for nitrogen stress response.4.Differentially expressed genes include 165 transcription factors.Among them,the top 7 genes with the highest up-regulated expression were LOB1,LOC101783857,anthocyanin regulating proteins C1,OFP1,IAA30,NAC73,and bHLH148;the top 7 genes with the highest down-regulated expression were bHLH041,ZAT8,and iron deficiency-induced transcription,respectively factors LOC101759395,ZAT12,WRKY62,WRKY70 and ZAT11.It is speculated that anthocyanin regulatory proteins C1 and bHLH148 participate in response to low nitrogen stress by up-regulating expression,and bHLH041,ZAT12,WRKY62,WRKY70 and ZAT11 may respond to low nitrogen stress by down-regulating expression.It was also identified that the stress-resistant genes WRKY54,AP2-EREBP transcription factors ERF53,ERF34,and LOC101778652(NAC79)were up-regulated under low nitrogen stress,and ERF3,ERF4,LOC101756256(NAC2),and LOC101777848(NAC72)were down-regulated.Maybe These genes are also involved in millet’s low nitrogen stress response.5.5 genes involved in nitrate transporter(LOC101782164),nitrite reductase(LOC101777206),glutamine synthetase(LOC101754854,LOC101772334)and cyanate ester lyase(LOC101775389)involved in the nitrogen metabolism pathway are up-regulated expression,and four genes,glutamic acid dehydrogenation enzymes(LOC101755619),nitrite hydratase(LOC101766965),carbonic anhydrase(LOC101763568,LOC191764398),were significantly down-regulated,and they worked together to transform nitrogen absorption and transfer.