The Loss Of OsMADS57 Gene Affect Rice Growth

Rice is one of the most important grain crops in China and nitrogen(N)is considered as an important limited factor affecting production of cereal crops.Rice roots can excrete O2 to surrounding soil and this can convert ammonium(NH4+)to nitrate(NO3-)in the process of nitrification at root surface or in rhizosphere.And rice roots are actually always exposed to a mixture of NH4+ and NO3-although the predominant species of mineral nitrogen(N)in the soil collected from the lowland rice field is NH4+.Therefore NO3-nutrition on the surface of rice roots is an important part of N nutrition of rice plants.Low and medium NO3-can stimulate the growth of the rice root,especially on lateral roots.How nitrate participate the rice root growth is unclear.In Arabidopsis the AtANRl gene participates the lateral root growth regulated by nitrate.In an attempt to get a better understanding of the root growth regulated by nitrate,we isolated and/or functionally characterize a MIKCc transcription factor encoding gene(OsMADS57)in rice in the present work.The main results acquired are listed as follows:?1)The homologous gene of Arabidopsis transcription factor encoding gene,AtANR1,was identified as OsMADS57 in rice(Oryza sativa L.).The expression level of the OsMADS57 gene in rice plant was ranked as:the blade>root>sheath.And higher expression level was observed in vegetative stage than in maturity stage.Compared with under N deficiency,the expression of MADS57 was significantly induced by nitrate nutrition rather than in ammonium nutrition.These indicated that the expression of MADS57 was induced by nitrate nutrition expecially by low concentration of nitrate.2)Hydroponic experiments were conducted to study the effects of series of nitrate concentrations on N uptake and root morphology in rice at the seedling stage.The results were listed as follows.The dty weight of shoot and root didn't change when nitrate concentration decreasing form 5 to 0.2 mM.However,when nitrate concentration dropped to 0.01 mM,the dry weight of shoot decreased significantly while that of root increased by 46%,At the same time,the length of seminal and adventitious roots enhanced remarkedly with nitrate concentration decreasing,while the density of lateral root for seminal and adventitious roots decreased significantly with nitrate level decreasing.And N concentration decreased with nitrate concentration decreasing.3)Hydroponic experiments were conducted to study the effects of low and high nitrate concentrations(0.2 and 5 mM NO3-)on root morphology in mads57 mutant and wild type at the seedling stage.Compared with wild type,the total root length in mads5 7 decreased markedly by 26%under 0.2 mM nitrate concentration.Further study showed that the decrease in root length result from the length of seminal and adventitious roots inhibited by 0.2 mM nitrate concentration.No difference in root morphology was recorded in mutant and wild type under 5 mM nitate nutrition.Field and pot experiments were conducted to analyse the morphology of mads57 mutant relative to wild type.The results showed that no difference was recorded in plant height between mutant anf wild type,while decreament of the seed rate was recorded in the mutant compared with the wild type.Interestingly,enhancement of tillers was observed in the mutant under sufficient N supply rather than under N deficiency.4)Compared with wild type,the expression level of NRT2.1,NRT2.2 and NRT2.3a was decreased in mads57 mutant.However,no difference was recorded between wild type and the mutant.