Analysis Of Physiological Mechanism Of Low Nitrogen Adaptation In Rapeseed And Arabidopsis Thaliana

As a large number of elements,nitrogen is crucial to the growth and yield of crops.Allotetraploid rapeseed(An An Cn Cn,2n=4x=38)has a higher demand for nitrogen fertilizer,but its nitrogen use efficiency is lower than that of cereal crops.Improving the nitrogen limitation adaptation(NLA)of crop is the key to improving crop nitrogen utilization efficiency(NUE)and reducing nitrogen fertilizer application in field production.Revealing the physiological and molecular genetic mechanisms of rape adaptation to nitrogen limitation is of great significance for NUE genetic improvement of rape and other crop varieties with complex genomes.A large number of studies have shown that the distribution of organic nitrogen is crucial to the maintenance of late plant growth and development,however,the core organic nitrogen transporters regulated by NLA are still unknown.Therefore,in this study,the brassica napus variety “xiangyou 15”,arabidopsis col-0(WT)and nla mutants were selected as the research objects combined with the analysis of physiology,genome and transcriptome,the adaptive strategies of rapeseed under low nitrogen stress were comprehensively studied,and the responses of wild type(WT)and nla mutants to low nitrogen conditions were analyzed by combining transcriptome and proteome,and the core organic nitrogen transporters targeted by NLA were predicted.The main results are as follows:1 Under low nitrogen conditions,rapeseed produced a series of adaptive reactions,such as decreased chlorophyll content,accumulated anthocyanin,reduced nitrate and total nitrogen concentration,decreased nitrate reductase activity(NR),enhanced glutamine synthase activity(GS),and increased nitrogen utilization efficiency(NUE).2 High-throughput transcriptmics showed that pathways associated with nitrogen metabolism and carbon fixation are significantly induced by low nitrogen.The gene expression involved in efficient nitrogen absorption,transfer,remobilization and assimilation changed significantly.3 Genome-wide identification and molecular characterization of the miR827-NLA1-NRT1.7 regulatory pathway revealed the important role of ubiquitin-mediated post-translational regulatory pathway in NLA.Transcriptional profiling assisted gene co-expression network identified BnaC5NLA1 as the core member of the NLA1 family,and the expression of BnaC5NLA1 is closely related to the low nitrogen tolerance of rape.4 Under low nitrogen conditions,nla mutants showed earlier aging than WT,with more chlorophyll decline,decreased anthocyanin accumulation,increased soluble sugar content,and more nitrogen transport from old leaves in the form of amino acids.5 High-throughput transcriptomics and proteomics analysis showed that low nitrogen inhibited the expression of genes involved in photosynthesis and protein synthesis and promoted proteolysis,and these changes were more significant in nla mutants than in WT.Transcriptmics and proteomics analysis showed that LHT1,responsible for amino acid transport,was significantly up-regulated only in nla mutants under low nitrogen conditions.These results indicated that NLA may target LHT1 to regulate the retransport of organic nitrogen.