The ribosomal protein RPS6A modulates auxin signalling and root development in Arabidopsis

Protein biosynthesis by the ribosome is a fundamental biological process in living systems. Recent studies suggest that ribosomal subunits also play essential roles in cell growth and differentiation beyond their roles in protein translation. The ribosomal subunit RPS6 has been studied for more than 50 years in various organisms, but little is known about its specific roles in a certain signalling pathway. In this study, we focused on the functions of Arabidopsis RPS6A in auxin-related root growth and development. The rps6a mutant exhibited a series of auxin-deficient phenotypes, such as shortened primary root length, reduced lateral root number, and defective vasculatures. Treatment of the rps6a mutant with various concentrations of auxin and its analogues did not restore the root defect phenotype, suggesting a defect in the auxin signalling pathway. Further cell biological and global transcriptome analyses revealed that auxin signalling was weakened in the rps6a mutant and that there was a reduced abundance of PIN-FORMED (PIN) auxin transporters. Our work provides insights into the role of the protein biosynthesis pathway involved in auxin signalling.