| As one of the most important grain crops in china,the rice cultivated area have been around over 30 percentage recent years.Knowing the significant role of rice to feed the whole country,China has accomplished that more than 98%rice grain yield are self-sufficient in2020.However,as the country’s urbanization development,land for cultivated functions faces serious challenges.Food security and cultivated land need more attention than ever.Effective tillers and panicle architecture are important constituent factors of yield.Rational application of nitrogen fertilizer can regulate rice architecture and improve yield.When plant hormone strigolactone were found to have the ability to suppress branching in higher plant,people have been identified several rice mutants of strigolactone pathway with dwarf and multi-tiller phenotype.Reaserches also showed that strigolactone synthesis and excretion are regulated by nitrogen supply,which indicated the coordination of strigolactone and nitrogen could influence rice development.Conbining physiological functions of strigolactone and nitrogen effect on rice,we could reveal deeper about the mechanism of nitrogen-strigolactone regulation and select some ideal architecture material to breed.By EMS（Ethylmethylsulfone）processing of rice seeds,we obtained a large mutant library.The mutants used in this paper is based on Wuyujing 7（WT）selected from the dwarf group.We found two lines differ in nitrogen sensitivity and identified that they are mutants of known d17 but mutated on two different sites.Diverse mutated sites of strigolactone synthetase gene D17 lead to disparity on phenotype and response on nitrogen treatment.The main results of the thesis are summarized as follows:1.Through high nitrogen supply and low nitrogen supply treatment on a group of EMS mutants,based on the phenotype response of nitrogen sensitivity,we selected two typical lines that shows their tiller numbers and yield are relatively differing in reacting to nitrogen treatment.ems2 is more sensitive to nitrogen supply than ems2 with sharp decline in tiller numbers and yield under low nitrogen condition.2.To confirm the nitrogen sensitivity of ems1 and ems2,we set four levels of nitrogen both in hydroponic culture and field experiment.The results show that the dynamic tiller number,dry weight,nitrogen accumulation and grain yield of ems2 are all more sensitive to nitrogen compared to ems1.Under low nitrogen condition the development of ems1 is less suppressed than ems2.Also they both showed decreased NUE compared to WT.3.After identification of ems1 and ems2,they were found to have different mutated base sites on Os CCD7.The mutation of ems1 caused a GAG to TAG transform at 1830 bp of the strigolactone synthetase Os CCD7 to lose function as TAG stoped translation ahead.Mutation at 2030 bp lead to an amino acid exchange that created ems2 mutant line.Exogenous GR24can recover the phenotype of ems1 and ems2 to WT indicated they are mutant of new d17lines.4.Expression levels of strigolactone synthsis genes D10 and D27 are significant higher in ems2 root than that in ems1.Expression levels of strigolactone signaling gene D3,ems1shows higher expression in shoot base than ems2.D53 also shows different expression in root of the two lines.In a word,strigolactone pathway genes are influenced by differen D17mutation sites ems1 and ems2 causing phenotype variations.5.Using 15N marked nitrogen to analyze nitrogen uptake and transport efficiency,the results suggested no difference between ems1 and ems2 on transport efficiency,but they are both significantly higher than WT.ems2 showed fast uptake of nitrogen under high nitrogen condition in short time indicating it is sensitive to high nitrogen supply.The genes associated with nitrogen absorption in ems2 were significantly higher in root expression than ems1 under high nitrogen conditions,and there was no difference in nitrogen assimilation genes expression at both high nitrogen and low nitrogen.After long-term transport distribution under low nitrogen supply,the concentration of nitrogen on the ground and root of ems1 was higher than that of ems2 and WT,which means ems1 could adjust better to low nitrogen. |
