Functional Relationships Of Arabidopsis Ribosomal Protein RPL23a Paralogues

Ribosome is an organelle without membrane.Its main function is to synthesize proteins.Ribosomes are composed of large subunits and small subunits,and each subunit is composed of ribosomal proteins and ribosomal RNAs(rRNAs).There are many kinds of ribosomal proteins,and the proteins composition of ribosome is different between plant species.Ribosomal protein is an important component of ribosome,mutation in ribosomal protein will seriously affect the normal function of ribosome.The absence of some key ribosomal proteins will lead to the disorder of normal life activities of cells,organ development defects and even death.Ribosomal proteins in plants are encoded by multiple genes belonging to the same gene family.Some of these homologous ribosomal proteins are functionally redundant,while others perform different functions in cells.The ribosomal protein RPL23astudied in this research is encoded by two ribosomal protein genes RPL23aA and RPL23aB.In this study,Arabidopsis thaliana was used to investigate the effects of RPL23aA and RPL23aB proteins on the growth and development of Arabidopsis.By comparing the sequences of RPL23aA and RPL23aB genes and their encoding proteins,we found that their gene sequences and protein sequences are highly similar.Through the phenotype observation of rpl23aa,rpl23ab,and RPL23aA/rpl23aa RPL23aB/rpl23ab,we found that the mutants with either homozygous or heterozygous mutation of RPL23aA gene exhibited developmental defective phenotypes,but to different degrees,whereas RPL23aB gene mutation did not cause any significant phenotype,indicating that RPL23aA plays a predominant role in these two paralogues.The severe developmental defects of rpl23aa/rpl23ab double mutants suggested that the RPL23agene family is very important for the normal physiological function of plant.EitherRPL23aA orRPL23aB gene driven by RPL23aA promoter in rpl23aa can rescue the phenotype of rpl23aa,indicating the phenotype of rpl23aa was indeed caused by the mutation of RPL23aA gene,and these two proteins may have equal function.GUS staining result that RPL23aA and RPL23aB genes were expressed in various tissues of plants,and the expression patterns of these two genes were basically the same,but the expression level of RPL23aB was slightly weaker than that of RPL23aA,which indicated that RPL23aA and RPL23aB are dosage-dependent genes.We also fused RPL23aA and RPL23aB genes with 35S promoter and transformed them into wild type Arabidopsis thaliana.It was found that some T₁ plants exhibited phenotypes including clustered inflorescence and bending pod.Results of q RT-PCR and western blotting showed that the transcription and translation levels of RPL23aA and RPL23aB were decreased in phenotypic individuals,suggesting that the phenotype may be caused by co-repression.