ORIGINAL ARTICLE

Role of Ribosomal Protein S6 in Maintaining Translational Integrity in Plants under Osmotic Stress

Regulation of protein synthesis is essential for cellular adaptation to environmental stress. In contrast to animals and yeast, plants lack several canonical mechanisms of rapid translational repression, suggesting the existence of alternative strategies for controlling ribosome activity. Increasing evidence indicates that discrete fragmentation of ribosomal RNA may represent one such mechanism in plant cells.

In this study, we examined the role of ribosomal protein S6 (RPS6) in stress-associated 18S rRNA fragmentation in Arabidopsis thaliana. Wild-type (Col-0) and rps6a knockout protoplasts were subjected to osmotic stress (250 mM NaCl). Ribosomal RNA integrity was assessed by denaturing polyacrylamide gel electrophoresis followed by Northern blot hybridization using probes specific to the 5′ and 3′ termini of 18S rRNA.

Osmotic stress induced significant accumulation of a 75-nt 5′-terminal fragment in wild-type cells. In the RPS6A knockout line, elevated basal levels of this fragment were observed even in the absence of stress. In contrast, the ~100-nt 3′-terminal fragment exhibited reduced abundance in the mutant background and showed distinct stress-dependent dynamics.

These findings demonstrate that RPS6 contributes to maintaining 18S rRNA structural integrity and differentially modulates region-specific fragmentation under osmotic stress. The results support a model in which discrete 18S rRNA fragmentation represents a ribosome-centered layer of translational regulation integrated with stress-responsive signaling pathways in plants.