Utilization And Evaluation Of Genetic Effects Of Nitrogen Metabolism Genes In Rice

Nitrogen is an essential element for plant development and growth.Applying proper amount of nitrogen fertilizer is one of necessary measures to obtain high yield in rice.However,excess nitrogen application has already led to severe environmental pollution.How to increase crop product and nitrogen use efficiency of crops is an important subject.In this study,we obtained five near-isogenic lines(NILs)each harboring one nitrogen metabolism gene from Nipponbare in the common background ZS97 and developed several pyramiding lines each containing three or four introduced nitrogen genes through molecular marker-assisted selection.Evaluation of these NILs and pyramiding lines in the gene expression and nitrogen use efficiency through hydroponic experiments with Nt4+,NO3-and NH4NO3 solutions.The main results are as follows:1.There are mutations in the promoter regions of five nitrogen metabolism genes between ZS97 and Nipponbare,which lead to significant differences of gene expression under NH4+and NO3-condition.The expression levels of ZS97 alleles of OsNADH-GOGAT1 and OsGDH1 were induced by NH4+ and NO3-and were significantly higher than that of Nipponbare alleles.On the contrary,the expression levels of Nipponbare alleles of OsAS2 and OsGS1 were significantly higher than that of ZS97 alleles.OsNRl was inhibited by NH4+,while induced by NO3 and the expression level of ZS97 allele was signifncantly higher than that of Nipponbare allele.There are also variants in coding regions of OsNRl,OsNADH-GOGATl and OsGSl;1 between Nipponbare and ZS97.Basing on two Indels in coding regions of OsNRl and 0sGS1;1,we developed two genic markers NR1-1 and GS1-1.2.Five near-isogenic lines in the common background of ZS97 were constructed by marker-assisted selection named NIL-OsNR1,NIL-OsNADH-GOGAT1,NIL-OsAS2,NIL-OsGDHl and NIL-OsGS1;1 We also developed 5 pyramiding lines with 3 or 4 above genes together(PY1-PY5)by a backcrossing and self-crossing scheme.3.Hydroponic experiments revealed that fresh weight(FW),dry weight(DW),chlorophyll content(CC)and total nitrogrn content(TNC)of NIL-OsNR1 under NH4NO3 and NO3-conditions were significantly higher than those of ZS97,indicating the Nipponbare allele of OsNR1 showed a higher NO3-use efficiency.FW,DW and CC of NIL-OsNADH-GOGAT1 were significantly higher than those of ZS97 under NO3-condition while CC was significantly lower than that of ZS97 under NH4+ condition,indicating that the OsNADH-GOGAT1 japonica Nipponbare allele had a higher N3-use efficiency and lower NH4+use efficiency than the indica ZS97 allele.The FW of NIL-OsAS2 under NH4NO3 condition was significantly higher than that of ZS97,indicating that OsAS2 japonica allele showed a higher NH4NO3 use efficiency.A segregating population analysis showed that OsAS2 was a potential gene affecting yield per plant(YPP).FW,DW,CC and TNC of NIL-OsGDHl under N03-,NH4+ and NH4NO3 conditions were significantly lower than those of ZS97,indicating the nitrogen use efficiency of Nipponbare OsGDHl was significantly lower than that of the indica allele.Plant height(PH)of NIL-OsGS1;1 under NH4+condition was significantly higher than that of ZS97,indicating OsGS1;'1 japonica allele had a higher NH4+use efficiency.However,FW,DW,CC and PH of gene pyramiding lines under three nitrogen conditions were significantly lower than those of ZS97,indicating that multiple japonica nitrogen genes pyramided into the indica variety ZS97 significantly decreased the nitrogen use efficiency.