Plant mitochondrial rps2 genes code for proteins with a C-terminal extension that is processed

Area of Science:

• Plant molecular biology
• Mitochondrial genomics
• Protein evolution

Background:

• The rps2 gene, encoding ribosomal protein S2, is located in the mitochondrial genome of monocots but absent in dicots.
• This suggests a gene transfer event from mitochondria to the nucleus in dicot evolution.

Purpose of the Study:

• To investigate the evolutionary fate of the rps2 gene in plants.
• To characterize the structure and expression of the rps2 gene in maize.

Main Methods:

• Gene identification and sequencing in Arabidopsis thaliana and maize.
• Analysis of gene transcription using transcript levels.
• Immunological detection of protein precursors and mature proteins.

Main Results:

• An Arabidopsis thaliana nuclear gene encoding mitochondrial RPS2 was identified, lacking a typical N-terminal targeting sequence.
• Two rps2 genes were found in the maize mitochondrial genome, both transcribed at varying levels.
• Maize RPS2 proteins exhibit long, non-conserved C-terminal extensions compared to bacterial counterparts.
• A large precursor protein is synthesized and processed to mature RPS2 associated with the mitochondrial ribosome.

Conclusions:

• The rps2 gene has undergone relocation to the nucleus in dicots and retained mitochondrial localization.
• Maize possesses unique mitochondrial rps2 genes with extended C-termini, indicating functional adaptation.
• Mitochondrial ribosomal protein S2 is synthesized as a precursor and processed within the mitochondrion.