Arabidopsis paralogous genes RPL23aA and RPL23aB encode functionally equivalent proteins

Area of Science:

• Plant molecular biology
• Genetics and genomics
• Ribosome biogenesis

Background:

• Ribosomal proteins (RPs) in plants are often encoded by small gene families, but functional diversification among family members is poorly understood.
• Arabidopsis thaliana possesses two paralogous genes, RPL23aA and RPL23aB, encoding cytoplasmic ribosomal proteins.
• Previous studies suggested functional divergence between RPL23aA and RPL23aB based on distinct phenotypes of knock-down and knock-out mutants.

Purpose of the Study:

• To investigate the functional equivalence and expression patterns of the RPL23a paralogous genes (RPL23aA and RPL23aB) in Arabidopsis thaliana.
• To clarify the roles of RPL23aA and RPL23aB in plant growth and development.

Main Methods:

• Characterization of T-DNA insertion mutants for both RPL23aA and RPL23aB.
• Analysis of non-allelic non-complementation in F1 progeny to assess gene dosage effects.
• GUS reporter gene expression analysis to determine tissue-specific expression patterns.
• Complementation studies using RPL23aB driven by the RPL23aA promoter.
• Bioinformatic analysis of publicly available RNA-seq data for expression profiling.

Main Results:

• A non-allelic non-complementation phenomenon revealed a dosage effect between RPL23aA and RPL23aB.
• Both RPL23aA and RPL23aB are expressed in most plant tissues.
• RPL23aB can functionally rescue the RPL23aA mutant phenotype, indicating functional equivalence of the proteins.
• RNA-seq data showed concerted expression of both paralogs, with RPL23aA consistently expressed at higher levels than RPL23aB.

Conclusions:

• The RPL23aA and RPL23aB proteins are functionally equivalent, challenging previous assumptions of divergence.
• RPL23aA plays a predominant role in planta due to its significantly higher expression levels compared to RPL23aB.
• The presence of both paralogous RPL23a genes may be essential for maintaining adequate ribosomal protein dosage in plants.