Screening Of Nitrogen Efficient Genes Related To Morphological And Physiological Plasticity Of Wheat

China is faced with the problem of excessive nitrogen application and low utilization rate in wheat production.The morphological and physiological plasticity of wheat is an important factor to reduce yield loss and improve resource utilization efficiency,and the plasticity is closely related to the expression and regulation of Expansin,WRKY,NAR,NRT and PSB gene families.Therefore,how to make full use of the morphological and physiological plasticity of wheat to maintain wheat yield under the premise of reducing nitrogen application rate has become an urgent problem to be solved.In this study,the leaf and root morphology,physiological parameters,nitrogen absorption and utilization,gene family expression and protein content of winter wheat seedlings under nitrogen starvation were investigated by hydroponic experiment.The morphological and physiological plasticity of wheat under nitrogen starvation was determined.Combined with bioinformatics,the relationship between the expression regulation of various genes and the morphological and physiological plasticity of wheat under nitrogen starvation was explored.Genes associated with improved nitrogen uptake and utilization were identified.This study can provide reference for identification of nitrogen efficient genes by transgenic methods,and provide theoretical guidance for rational reduction of nitrogen application,full utilization of morphological and physiological plasticity of winter wheat,and improvement of nitrogen use efficiency.The main results are as follows:1.Morphological and physiological plasticity of wheat seedlings under nitrogen starvationDuring nitrogen starvation,wheat seedlings compensated for the adverse effects of nitrogen deficiency through the plasticity of root indexes and photosynthetic physiological indexes,thus maintaining the normal growth of wheat.The results showed that nitrogen starvation inhibited the growth of wheat seedling leaves,and the plant height,leaf weight and leaf area of 1,3,5 and 7 days after nitrogen starvation treatment were all lower than normal nitrogen treatment,nitrogen starvation on the fifth day was significantly lower than normal nitrogen treatment.Nitrogen starvation to promote the growth of wheat seedling root,root length,root surface area,root volume,root weight of 1,3,5 and 7 days after nitrogen starvation treatment were all greater than normal nitrogen treatment,root indexs on the fifth day of nitrogen starvation are significantly higher than normal nitrogen treatment.The number of cells in root apical meristem area on the fifth day of nitrogen starvation was significantly higher than normal nitrogen treatment,which conducive to the growth of root.The photosynthetic rate and stomatal conductance of wheat seedlings under nitrogen starvation increased first and then decreased,and were significantly higher than normal nitrogen treatment on the fifth day of nitrogen starvation,and began lower than normal nitrogen treatment on the fifth day of nitrogen starvation.2.Identification and screening of nitrogen efficient genesThe molecular response mechanism of wheat under nitrogen starvation condition can provide basis for screening nitrogen efficient genes in the future.In this study,a total of 38,32,5,4 and 12 differentially expressed genes of Expansin,WRKY,NAR,NRT and PSB in response to nitrogen starvation were identified using bioinformatics methods based on transcriptomic and proteomic databases from roots and leaves treated with N1 and N0.The expression levels of 24,4,2,4 Expansin,WRKY,NAR and NRT differentially expressed genes were increased in roots and leaves under nitrogen starvation.The expression levels of 7,13,3 Expansin,WRKY and NAR differentially expressed genes were decreased in root tissues.The expression levels of 4,10,2,1 Expansin,WRKY,NAR and PSB differentially expressed genes increased under nitrogen starvation.The expression levels of 3,9,2,11 Expansin,WRKY,NAR and PSB differentially expressed genes were decreased in leaves.Then we found the position,chromosome distribution and gene structure of these differentially expressed genes in the evolutionary tree.According to the phylogenetic tree,Expansin,WRKY,NAR,NRT and PSB differentially expressed genes could be divided into 3,3,2,3 and 12 subfamilies.The results of chromosome mapping showed that five gene families were distributed on 17,16,3,4,13 of wheat chromosome respectively.The gene structure analysis showed that the number of exons of 5 different gene families ranged from2-5,1-5,2-4,1,1-5 respectively.GO enrichment and KEGG enrichment showed that 24 Expansin genes（EXPA31,EXPA14,EXPA24 and EXPA9）,whose expression levels were significantly increased in roots under nitrogen starvation,were enriched in components related to cell wall extension function.One WRKY71 gene and one WRKY24 gene were enriched in ABA or GA signaling pathway.Two NAR7 genes with significantly decreased expression level in leaves and four NRT genes with significantly increased expression level in roots were enriched in nitrogen metabolism pathway.Eleven PSB genes（PSB27,PSB28,PSBD,PSBM）with significantly decreased expression and one PSBR gene with significantly increased expression were enriched in photocooperative photosystem II pathway.3.Nitrogen efficient genes related to morphological and physiological plasticity of wheat seedlingsExpansin,WRKY and NRT gene families maybe associated with root morphological changes of wheat seedlings during nitrogen starvation.One WRKY71 gene with significantly reduced expression in roots under nitrogen starvation inhibited ABA signaling pathway and inhibited root growth.Expansin and NRT genes with significantly higher expression levels in roots ultimately promoted the development of wheat seedling roots.Expansin genes mainly EXPA31,EXPA14,EXPA9 and EXPA24 induced the extension of root cell wall,may promoted root elongation,and then increased root surface area and promoted nitrogen absorption.Among NRT genes,NRT2.1,NRT2.2,NRT2.3 and NRT2.4 promote the transport of nitrate into cells in root nitrogen metabolism pathway,may promote the root absorption of nitrogen,and it may conducive to root growth.NAR and WRKY genes families maybe associated with leaf morphological changes of wheat seedlings during nitrogen starvation.The NAR7 gene with significantly reduced expression in the lower leaves of nitrogen starvation inhibited the reduction of nitric acid to nitrite in the nitrogen metabolism pathway,and may reduced the uptake of nitrogen by leaves,which was not conducive to leaf growth.One WRKY24 gene with significantly reduced expression in leaves inhibited ABA and GA signaling pathways,which may inhibit leaf development and increase of leaf area,and reduce photosynthetic area,thus affecting nitrogen uptake in leaves.Photosynthesis of wheat seedlings under nitrogen starvation may be related to PSB genes families.One PSBR gene with significantly increased expression level may promoted photosynthesis,while PSB27,PSB28,PSBD and PSBM genes with significantly decreased expression level inhibited photosynthesis and reduced photosynthetic rate.