Decoding Plant Ribosomal Proteins: Multitasking Players in Cellular Games

Abstract

Ribosomal proteins (RPs) were traditionally considered as ribosome building blocks, serving exclusively in ribosome assembly. However, contemporary research highlights their involvement in additional translational roles, as well as diverse non-ribosomal activities. The functional diversity of RPs is further enriched by the presence of 2-7 paralogs per RP family in plants, suggesting that these proteins may perform distinct, specialized functions. The spatiotemporal expression of RP paralogs allows for the assembly of unique ribosomes (ribosome heterogeneity), enabling the selective translation of specific mRNAs, and producing specialized proteins essential for plant functioning. Additionally, RPs that operate independently of ribosomes as free molecules may regulate a wide range of physiological processes. RPs involved in protein biosynthesis within the cytosol, mitochondria, or plastids are encoded by distinct genes, which account for their functional specialization. Notably, RPs associated with plastid or mitochondrial ribosomes, beyond their canonical roles in these organelles, also contribute to overall plant development and functionality, akin to their cytosolic counterparts. This review explores the roles of RPs in different cellular compartments, the presumed molecular mechanisms underlying their functions, and the involvement of other molecular factors that cooperate with RPs in these processes. In addition to the new RP nomenclature introduced in 2022/2023, the old names are also applied.

Keywords: plant cellular ribosomal proteins; plant development; ribosomal protein paralogs; ribosome heterogeneity; stress response.

Figure 1

Roles of cellular ribosomal proteins (RPs) in plant functioning. Cytosolic, mitochondrial, and plastid RPs collectively contribute to overall plant development, reproduction, and responses to biotic and abiotic stress factors (the circle encompasses cellular compartments and representative RPs involved in these processes). Additionally, mitochondrial and plastid RPs are specifically involved in the development and functioning of their respective organelles. Selected RPs functioning in A. thaliana (discussed also in this review) are depicted in this illustration with their names according to the new nomenclature of RPs, as well as corresponding gene locus IDs [5,6]. Created with BioRender/i71j550.

Figure 2

Overview of ribosomal protein (RP) functions. RPs, which form the small (SSU) and large (LSU) ribosomal subunits, are essential for ribosomal functions, primarily the translation of mRNAs encoding both housekeeping proteins and proteins with specialized roles (depicted on the left side of the illustration). Beyond their roles within ribosomes, RPs can also operate independently, performing a variety of non-ribosomal functions (shown on the right side of the illustration). Some cytosolic RPs of SSU and LSU involved in these functions in A. thaliana, also discussed in this article, are represented by their updated names and corresponding gene locus IDs [5,6] in this illustration. Created with BioRender/v50y957.

Figure 3

Composition of cytosolic, plastid/chloroplast, and mitochondrial ribosomes in A. thaliana. The total number of ribosomal proteins (RPs), including RP paralogs, as well as the number of RPs encoded by the nuclear and organelle genomes, are presented. The rRNA components of each ribosomal subunit are also specified; LSU–large ribosomal subunit, SSU–small ribosomal subunit. Ribosomal data according to literature [6,39,42,61,62]. Created with BioRender/x23t722.