Auxin/NAP1 RELATED PROTEIN 1 and 2 interplay supports stem cell niche maintenance in Arabidopsis root

Stem cells maintain tissue homeostasis and regeneration in multicellular organisms, including plants and mammals. Several pieces of evidence suggest a triangular connection among stem cells, genome integrity and the plant hormone auxin. Indeed, optimal genome integrity is essential for stem cell activity, and in plants, auxin was shown to determine root stem cell identity and to have a positive effect on genome stability. However, for the latter aspect, the mechanism is still unknown. To determine the molecular and cellular events linking auxin, stem cells and genome integrity, I exploited the A. thaliana root as a model. A. thaliana is particularly suited to the study of stem cells because of its stereotyped root cell division pattern that allows following single stem cells properties and fate. By in silico and in vivo analyses I identified the histone chaperones NAP1-RELATED PROTEIN 2 and 1 (NRP2 and NRP1) as auxin targets which participate in preventing DNA damage and cell death. At the organismal level, the data from this work showed that the depletion of both proteins in the root stem cell niche leads to alteration in stem cell functionality, reduced meristem size and root length, suggesting their requirement for root development. Finally, the discovery that auxin can modulate gene expression of A. thaliana NRP2 and NRP1 human orthologue SET/TAF-Iβ, involved in chromatin remodelling, provides new intriguing evidence of the regulation of the same factors in both plant and animal cells by the same plant phytohormone.