Rerouting of ribosomal proteins into splicing in plant organelles

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Abstract
Production and expression of RNA requires the action of multiple RNA-binding proteins (RBPs). New RBPs are most often created by novel combinations of dedicated RNA-binding modules. However, recruiting existing genes to create new RBPs is also an important evolutionary strategy. In this report, we analyzed the eight-member uL18 ribosomal protein family in Arabidopsis. uL18 proteins share a short structurally conserved domain that binds the 5S ribosomal RNA (rRNA) and allows its incorporation into ribosomes. Our results indicate that Arabidopsis uL18-Like proteins are targeted to either mitochondria or chloroplasts. While two members of the family are found in organelle ribosomes, we show here that two uL18-type proteins function as factors necessary for the splicing of certain mitochondrial and plastid group II introns. These two proteins do not cosediment with mitochondrial or plastid ribosomes but instead associate with the introns whose splicing they promote. Our study thus reveals that the RNA-binding capacity of uL18 ribosomal proteins has been repurposed to create factors that facilitate the splicing of organellar introns. Significance Ribosomal proteins (RPs) are essential structural components of ribosomes. In many instances, RPs are encoded in small families of genes, suggesting possible neofunctionalization for some family members. This is the case of the uL18 family of proteins that developed during plant evolution and which is composed of eight members in most Angiosperms. Our study shows that two members associate with organellar ribosomes while two other uL18-Like proteins have become intron-specific splicing factors acting in mitochondria and plastids, respectively. Our study shows that the RNA binding capacity of RPs can be diverted to create factors acting in intron splicing.
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  • Agence Nationale de la Recherche (ANR-16-CE11-0024-01)

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