Recombinant Arabidopsis thaliana 60S ribosomal protein L2, mitochondrial (RPL2)

Gene Structure and Evolutionary Context

The mitochondrial ribosomal protein L2 (RPL2) in Arabidopsis thaliana exhibits a fragmented evolutionary history. Unlike monocots like rice, where rpl2 exists as a single mitochondrial gene, eudicots like A. thaliana have undergone gene fission events. The ancestral rpl2 split into two segments: a truncated mitochondrial 5′ rpl2 and a nuclear 3′ rpl2 . In A. thaliana, the mitochondrial genome retains the 5′ portion of rpl2, while the 3′ portion was transferred to the nucleus early in eudicot evolution and remains functional . This dual-compartment gene structure necessitates coordinated expression for proper mitochondrial ribosome assembly.

Key Features of A. thaliana RPL2

• Mitochondrial Component: The truncated mitochondrial 5′ rpl2 (212 codons in A. thaliana) is a pseudogene in many core eudicots but retains transcriptional activity in some species .

• Nuclear Component: The nuclear 3′ rpl2 encodes the functional C-terminal domain required for ribosomal assembly .

• RNA Editing: The mitochondrial transcript undergoes C-to-U RNA editing at position 212 (nonsilent site), altering amino acid identity (e.g., Pro → Leu) and influencing ribosomal function .

Functional Role in Mitochondrial Translation

RPL2 is essential for mitochondrial ribosome assembly and respiratory chain biogenesis. In A. thaliana, RPL2 interacts with other ribosomal proteins (e.g., RPS19) and is critical for:

• Intron Splicing: Required for splicing group II introns in mitochondrial transcripts like rpl2 and ccmF(C) .

• Cytochrome c Maturation: Facilitates the biogenesis of c-type cytochromes, which are vital for electron transport .

• Editing Efficiency: Polymorphisms in editing efficiency between A. thaliana accessions (e.g., Columbia vs. Landsberg erecta) correlate with mitochondrial translation fidelity (Table 1) .

Table 1: Editing Efficiency of Mitochondrial Sites in A. thaliana

Genetic Regulation and QTL Mapping

Natural variation in mitochondrial editing efficiency is governed by quantitative trait loci (QTL). Key findings include:

• Major QTL: 12 major QTL were identified on chromosomes 1–5, regulating editing efficiency of rpl2-212 and other ribosomal protein transcripts (Table 2) .

• Dominance Patterns: Nonsilent editing sites (e.g., rpl2-212) exhibit dominance, while silent sites show additivity .

Table 2: Major QTL Associated with Editing Efficiency

Future Directions

Recombinant A. thaliana RPL2 could address unresolved questions:

• Structural Analysis: Cryo-EM studies (as done for human LRPPRC ) could resolve RPL2’s role in mRNA recruitment.

• Editing Mutants: Engineering rpl2 editing variants (e.g., Pro212Leu) may clarify its impact on ribosome stability.

• Cross-Species Rescue: Expressing A. thaliana RPL2 in species with nuclear-only rpl2 (e.g., legumes) could test functional conservation .