Preliminary Study On Cell Cycle-dependent Kinases Regulating The Nuclear Replication Of Nodule Cells

Nitrogen,as one of the important elements required for life,is of great significance for plant growth,development and reproduction.Biological nitrogen fixation is able to efficiently fix atmospheric nitrogen for plants.The legume-rhizobia symbiosis system is the most practical example of biological nitrogen fixation.Legumes and rhizobium form a special tissue-nodules,which is the main site for nitrogen fixation.Nodule cell endoreplication is required for nitrogen fixation.Endoreplication,a special cell cycle,is affected by a variety of cell cycle regulators,and cyclin-dependent kinases(CDK)might be one of the important regulators.CDK combines with cyclin to form heteropolymers,which regulate various phases of the cell cycle.However,it is not clear how CDK regulates the nodule cell endoreplication.Therefore,we conducted preliminary screening and research to the role of CDK during nodule cell endoreplication.The main findings are as follows:1.The online database was used to analyze the gene expression,and four CDKs:Medtr1g075610(CDK1.2),Medtr4g007750(CDK4.1),Medtr4g086450(CDK4.4),and Medtr4g118780(CDK4.8)was expressed at lower level in nodules,but highly level in roots.2.The expression patterns of CDK1.2 and CDK4.1 in nodules were similar by q RT-PCR and GUS staining.They were expressed in both primordia and immature nodules,but only in zone ? and zone ? of mature nodules.CDK1.2 promoter and CDK4.1 promoter were segmented and found that the cis-acting element related to expression of CDK4.1 in nodules were located at-2000 bp to-1000 bp.3.The fusion expression of CDK1.2-GFP and CDK4.1-GFP was driven by the DNF1 promoter,which is highly expressed in nodules.Inoculated with Rhizobium ABS7,it is find that the nodules of overexpression of CDK4.1 are slightly elongated white nodules and the nitrogen-fixing ability of rhizobia is significant differences by rhizobium RM 1021 nif H::GUS.When overexpressed,CDK4.1 is mainly accumulated in the nucleus of the nodules cell.The phenotype of overexpressed of CDK1.2 is similar to wild type-pink cylindrical nodules,and CDK1.2 is accumulated in the nucleus of the nodules cell.This study,a preliminary study on the mechanism of endoreplication of Medicago truncatula nodules,found that CDK4.1 is expressed in both primordia and immature nodules,but only in zone ? and zone ? of mature nodules.When overexpressed,CDK4.1 is accumulated in the nucleus of the nodules cell and led to exclusively white spherical or slightly cylindrical nodules on which an occasional pale pink nodule could be observed.CDK1.2 is expressed in both primordia and immature nodules,but only in zone ? and zone ? of mature nodules.When overexpressed,CDK1.2 is accumulated in the nucleus of the nodules cell.The overexpression of CDK1.2 developed pink cylindrical nodules.This study lays the foundation for further exploring the effect of CDK on the endoreplication of nodules.