Arabidopsis regeneration from multiple tissues occurs via a root development pathway

Unlike most animal cells, plant cells can easily regenerate new tissues from a wide variety of organs when properly cultured. The common elements that provide varied plant cells with their remarkable regeneration ability are still largely unknown. Here we describe the initial process of Arabidopsis in vitro regeneration, where a pluripotent cell mass termed callus is induced. We demonstrate that callus resembles the tip of a root meristem, even if it is derived from aerial organs such as petals, which clearly shows that callus formation is not a simple reprogramming process backwards to an undifferentiated state as widely believed. Furthermore, callus formation in roots, cotyledons and petals is blocked in mutant plants incapable of lateral root initiation. It thus appears that the ectopic activation of a lateral root development program is a common mechanism in callus formation from multiple organs. Four sets of biologically independent tissue samples were collect for root, cotyledon and petal explants just after being excised from plants (d0) or after ten days on callus-inducing medium (CIM, d10). Samples derived from the same organ were co-hybridized in the array experiments. Dyes used for labeling the RNA populations derived from the individual samples were switched in the replicate experiments to reduce dye-related artefacts.