Transcriptome Analysis Of A Maize Single Segment Substitution Line With High Nitrogen Utilization Efficiency Under Low Nitrogen Stress

In this study,a maize single segment substitution line SSSL10.04 containing nitrogen utilization efficiency QTL and its recurrent parent Xu 178 were cultured in LN and HN conditions by the technique of nutrient solution cultivation.Transcriptome profiling by RNA sequencing was performed on leaf and root samples collected after different N treated.The differentially expressed genes in the leaves and roots between the two lines in response to low-nitrogen stress were analyzed respectively.Moreover,the molecular basis of SSSL10.04 mediated nitrogen utilization efficiency was explored using transcriptome profiling.The main results were listed as follows:1.Under the low nitrogen condition,SSSL10.04 showed higher biomass and nitrogen accumulation,as well as significant higher nitrogen use efficiency in shoots than Xu178.The root length,root surface area and root volume of SSSL10.04 were all greater than Xu178.2.The clean reads of transcriptome sequencing were 21261777~35651871,and69.98%~76.19% of the sequences could be mapped to the genome of maize B73.Using HN treatment as a control,the gene expression level of maize treated with LN was up-regulated or down-regulated by 2 or more,and p<0.05 was used as a screening condition for differential genes.The 3933 and 2122 differential genes were obtained from leaves and roots of SSSL10.04,and 3516 and 2278 differential genes in leaves and roots of Xu 178 were obtained.3.Analysis of the overall differentially expressed genes between HN and LN in SSSL10.04 and Xu178 showed that the common responses involving low nitrogen stress on leaves were photosynthesis and carbohydrate metabolism according to the GO annotation.While in the roots,the transport of substances,carbohydrate metabolism and antioxidant processes were enriched.All these results indicated that,in spite of different genotypes,a common defense response was owned by the SSSL and its recurrent parent,and the common growth and metabolites were affected by nitrogen deficient.4.Gene Ontology analysis of the specifically up-regulated DEGs in SSSL10.04 and Xu178 showed that,compared with Xu 178,more upregulated genes involved in antioxidant,phytohormones synthesis and material transport were significantly enriched in SSSL 10.04 leaves under low nitrogen stress,and more up-regulated genes involved in respiration,antioxidant processes,and amino acid metabolism were significantly enriched in the root.5.The specifically up-regulated genes in the substitutional segment of SSSL10.04 were mainly involved in carbohydrate metabolism and amino acid metabolism,etc.The unknown function of specifically up-regulated genes in the substitutional segment of SSSL10.04 is worth further studying.Above all we speculate SSSL10.04 possessed a stronger adaptive mechanism for low nitrogen stress.The stronger antioxidative capacity protects tissue from damage caused by excessive active oxygen accumulation under prolonged low nitrogen stress,and stronger respiration in the root system provides more energy for the transport and synthesis of its materials.Moreover,enhanced amino acid metabolism promoted the redistribution of nitrogen in the body,which ensured a higher nitrogen utilization efficiency of SSSL10.04 in low nitrogen condition.