Regulatory Effect Of Ostir1,a Putative Auxin Receptor,on Rice Architecture,Root Morphology And Nitrogen Nutrition

Auxin acts as an essential regulator in many plant developmental processes,transferring information over both long and short ranges.Results from Arabidopsis showed that,auxin regulates downstream genes’ transcription level through auxin signaling module including Fbox proteins of the TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX(TIR1/AFB)family,members of the Aux/IAA transcriptional repressor family and transcription factors of the AUXIN RESPONSE FACTOR(ARF)family.TIR1/AFB,auxin receptors,participate auxin signaling pathway to regulate whole plant growth stage.However,few have been reported in other plant species such as rice.Grain yield depending on high amount of fertilizer application has brought serious environmental problem in China.In 2015,Ministry of Agriculture and Rural Affairs put forward the action plan of "Fertilizer Reduction and Efficiency Improvement".How to keep grain yield in the action plan is our major task.Our previous results showed that exogenous application of auxin can improve plant growth.Our scientific hypothesis is that,if auin receptor is overexpressed in rice plants,will overexpression lines have similar grain yield under low N supply to wild-type plants under high N supply?1、OsTIR1 is localized on chromosome 5.Sequence alignment between genomic and cDNA sequences showed that OsTIR1 has 3 exons and 2 introns.Results from subcellular localization showed that OsTIR1 is located at nucleus.Results from RT-qPCR analysis showed that,although OsTIR1 is constitutively expressed in plant organs during whole plant growth stage,OsTIR1 is highly expressed in shoot base and topmost leaf.2、Overexpresion of OsTIR1 increased rice growth including tiller number and grain yield.Field experiments were conducted in Hainan and Nanjing to evaluate effect of OsTIR1 overexpression on rice plant growth.Compared with wild-type(WT)plants grown in Hainan,overexpression of OsTIR1 lines(OE,T0 generation)had more tiller numbers and larger grain seeds,and thus grain yields of OE plants were superior to WT plants.Compared with WT plants grown in Nanjing,OE lines(T1 generation)had more tiller numbers and larger grain seeds under two N rates and thus grain yields and harvest index of OE plants were higher than WT plants.3、Overexpression of OsTIR1 increased N content in rice grains and N accumulation in rice plants.Compared with WT plants grown in Nanjing,OE lines(T1 generation)had higher N content in rice grains;high content in rice grains in combination with more biomass in OE than in WT ultimately led to 55%-increment of N accumulation in OE plants relative to WT plants.4、Overexpression of OsTIR1 increased formation of adventitious and lateral toots.Compared with WT plants grown in hydroponic culture,OE lines(T1 generation)had shorter seminal and adventitious roots.However,a greater number of adventitious root and higher lateral root density were observed in OE lines in comparison with WT plants.In conclusion,overexpression of auxin receptor OsTIR1 not only affected root formation,tillering and grain growth,but also affected N accumulation in rice plants.These help to illustrate OsTIR1 gene function in rice plant.