Function Analysis Of OsMADS27 Predominantly Expressed In Rice Root

As the vegetative important organ,the root system architecture is not only involved in the acquisition of water and nutrient,but also is the important place for material synthesis,assimilation and transition,and the bridge for substance exchange.The root system architecture is closely related to the development of above-ground part,and also has a crucial influence on agronomic characters in crops.Therefore,it is very essential to understand the molecular mechanism underlying the root growth and development process and improve the root system architecture in rice.The transcription factors of MADS-box family are found to be involved in the regulation of cell signal transduction and organ developmental processes in plant.ANR1,a NO₃^--inducible Arabidopsis gene,encodes a member of the MADS box family of transcription factors.OsMADS27,a homologue of ANR1 in rice and belongs to the AGL17-clade,is mainly expressed in the primary root,lateral root and lateral root primordium.In this study,we focused on investigating the biological functions of OsMADS27 by reverse genetics.The main research contents and results are as follows:（1）Biological functions of OsMADS27 in growth and development of rice plantsTo study the influence of OsMADS27 on the development of rice plants,OsMADS27 overexpression vector 35S::OsMADS27 was constructed and genetically transformed into rice calli to generate OsMADS27 overexpression transgenic plants.At seedling stage,OsMADS27 overexpression lines showed a remarkable decrease in the shoot growth and primary root elongation,whereas exhibited a significant increase in lateral root number and density in 1/2 MS medium,compared to wild type.In addition,the tillering number was also enhanced in overexpression plants.At mature stage,the heading was delayed in overexpression plants,which also showed a great reduction in the seed germination rate,in comparision of wild type counterparts.This result indicated that OsMADS27 plays an important role in growth and development in rice plants.（2）The role of NO₃^-in the lateral root development regulated by OsMADS27In view of the significance role of NO₃^-in the lateral root development and the fact that OsMADS27 is an ANR1 homologue in rice,we investigated the roles of OsMADS27 in NO₃^--regulated lateral root development.There was no significant difference in the root system architecture between OsMADS27 overexpression lines and wild type under NO₃^—deficient conditons（0 or 0.1 mM NO₃^-）.However,under higher NO₃^-concentration conditions,OsMADS27 overexpression lines showed a significant increase in lateral root number and a reduction in primary root length,compared to wild type.This result suggested that OsMADS27 overexpression lines were more sensitive to external NO₃^-supply in the regulation of lateral root and primary root development than wild type.Moreover,OsMADS27 overexpression plants accumulated much more NO₃^-than wild type,with corresponding higher expression levels of nitrate transporter genes.（3）The role of ABA in the lateral root development regulated by OsMADS27Considering that the expression of OsMADS27 was markedly induced by exogenous ABA,OsMADS27 overexpression lines and wild type were grown in the medium containing 1.5μM ABA to investigate the response of root system architecture to exogenous ABA.The primary root length and lateral root density were significantly reduced in OsMADS27 overexpression lines as well as wild type plants under ABA treatment,compared to the counterparts grown under normal growth conditions.However,OsMADS27 overexpression lines exhibited more sensitive to ABA than wild type,and also accumulated higher levels of ABA in roots.Furthermore,yeast two-hybrid assay showed that OsMADS27 interacted with OsSLR1,a repressor of GA signaling pathway,and OsSLR1 also interacted with OsABI5.Taken together,these data showed that OsMADS27 might regulate growth and development of rice through ABA signaling pathway.（4）The role of ABA in the process of OsMADS27 regulating lateral root development in a NO₃^—dependent mannerUnder 0.1 and 10 mM NO₃^-concentration conditions,OsMADS27 overexpression lines accumulated higher levels of ABA in roots than wild type.However,OsMADS27overexpression lines accumulated lower levels of ABA than wild type under 0 mM NO₃^-conditions,which indicated that NO₃^-can reduce ABA levels in wild type,whereas elevated ABA accumulation in OsMADS27 overexpression lines,with the increase in NO₃^-concentration.Moreover,OsMADS27 overexpression plants had higher expression levels of ABA synthesis genes and lower expression levels of ABA degradation genes,with corresponding higher levels of ABA accumulation.This result suggested that ABA might have a key role in the lateral root development regulated by OsMADS27 in a NO₃^—dependent manner.（5）The tolerance to abiotic stress of OsMADS27 overexpression linesUnder NaCl treatment,OsMADS27 overexpression lines had a lower decrease rate of lateral root number and primary root length than wild type,compared to the counterparts under the normal conditions.Thus the roost system architecture of OsMADS27 overexpression lines exhibited better performance than wild type under salinity.In addition,there was a significant difference in the increment rate of lateral root number as well as primary root length between OsMADS27 overexpression lines and wild type under PEG6000 treatment,and OsMADS27 overexpression lines showed higher lateral root density and longer primary root than wild type.Together,these results indicated that OsMADS27 might play an important role in the tolerance to abiotic stress.