Deficiency of Arabidopsis SMO2 triggers an ANAC082-Dependent pathway to regulate root apical meristem

Root apical meristem (RAM) maintains sustained root development, which is intricately coordinated by a series of biological processes integrating internal and external cues. Here, we present evidence that SMALL ORGAN 2 (SMO2) is required for the maintenance of RAM. Deficiency of SMO2 resulted in disorganization of the stem cell niche (SCN) and the presence of dead cells in RAM, independent of DNA damage. Moreover, following chemically induced wounding, excision of root tips, or removal of whole roots, the regeneration capacity of smo2 mutants was dramatically lower than that of wild-type plants. Mechanistically, SMO2 is necessary for 18S rRNA methylation at position G1581, which may be associated with abnormal ribosome profiles in smo2 mutants. Further analysis showed that deficiency of SMO2 markedly reduced the translation efficiency of genes involved in polar auxin transport, thereby reducing auxin accumulation in the RAM. Surprisingly, an additional deletion of ANAC082, which encodes a known transcriptional mediator of ribosomal stress-induced developmental adaptations, effectively restored the disordered SCN and cell death phenotypes in smo2 mutants. Collectively, our findings demonstrate that SMO2-mediated translational regulation plays an important role in auxin accumulation in root tips. This process appears to be essential for sustaining RAM activity, as indicated by the structural disorganization of root tips in smo2 mutants. Notably, this phenotypic manifestation is mechanistically dependent on ANAC082.