Dosage Sensitivity of RPL9 and Concerted Evolution of Ribosomal Protein Genes in Plants

Area of Science:

• Molecular Biology
• Plant Genetics
• Evolutionary Biology

Background:

• Higher eukaryotes possess complex ribosomes with numerous proteins, often encoded by multiple genes in plants.
• Duplicate genes can ensure sufficient protein dosage or exhibit specialized, non-redundant functions.
• The RPL9 gene family in Arabidopsis thaliana includes closely related RPL9B/RPL9C and a divergent RPL9D.

Purpose of the Study:

• To investigate whether divergent members of the RPL9 gene family in Arabidopsis thaliana are dosage-sensitive or have non-overlapping functions.
• To understand the evolutionary dynamics of ribosomal protein gene families in Brassicaceae and angiosperms.

Main Methods:

• Analysis of mutations in RPL9C and RPL9D genes.
• Phylogenetic analysis of RPL9, RPL4, RPL5, RPL27a, RPL36a, and RPS6 gene families in Brassicaceae.
• Phylogenetic analysis of RPL9 genes across angiosperm species.

Main Results:

• Mutations in RPL9C and RPL9D cause developmental delays; loss of both is embryo lethal, confirming dosage sensitivity and redundancy.
• Phylogenetic analyses show retention of multicopy ribosomal protein genes post-whole genome duplication in Brassicaceae.
• Evidence of tandem duplication, deletion, and gene conversion within these families was observed.
• Angiosperm RPL9 gene trees suggest convergent evolution, with species-specific genes being more closely related.

Conclusions:

• Ribosomal protein gene retention after whole genome duplication contributes to family expansion.
• Small-scale genomic rearrangements influence copy number and drive concerted evolution of dosage-sensitive genes.
• The RPL9 gene family exemplifies the interplay between gene duplication, dosage sensitivity, and evolutionary dynamics in plants.