Root branching is not induced by auxins in Selaginella moellendorffii (Front Plant Sci)

Auxin is crucial for root development across angiosperms. All the auxin signal transduction pathway components are conserved in land plants, but their role is still not completely clear in early diverged lineages. Here, Fang et al. present a comprehensive analysis of exogenous auxin addition and polar transport inhibitor effects in the root development of Selaginella moellendorffii, a representative lycophyte. It might be expected that auxin has an impact on root development, particularly through meristem bifurcation in dichotomous branching. Surprisingly, the main result of this paper is that exogenous auxin affects root cell elongation but not root cell precursor formation nor branching. Despite auxin increasing root branching in the long term as was shown previously (10.1111/nph.12183), no differences were found in the time needed for the first bifurcation, suggesting that the long-term effect could be indirect. Plants transiently exposed to the hormone or treated with inhibitors are similar to controls, indicating that the early stage of root branching is independent of auxin. This paper is an example of the importance of sharing “negative” results and also points out that auxin’s roles may be not conserved in all plant species in the same way. (Summary by Facundo Romani).  Front. Plant Sci. 10.3389/fpls.2019.00154