Molecular signals for regeneration ($)

Every gardener knows that pulling off a shoot is not sufficient to kill a plant. Plants are able to reprogram cells in order to regenerate missing tissues. Pulling off a shoot removes photosynthetic tissues, but the root responds by activating chloroplasts to take over this role. Kobayashi et al. (Plant Physiol. 10.​1104/​pp.​16.​01368) examine the signals involved in chloroplast activation in roots following shoot removal; wound responses, cytokinin increase and auxin depletion all contribute to this reprogramming.  To a large extent, regeneration involves activating differentiation pathways. Previously, nuclear accumulation of the transcription factor IYO was shown to trigger cell differentiation. Muñoz et al. (Plant Cell 10.​1105/​tpc.​16.​00791) identified a nuclear import protein RIMA involved in nuclear accumulation of IYO; this nuclear import triggers auxin-irreversible cell differentiation in Arabidopsis. Furthemore, that fact that IYO is excluded from the nucleus in xylem-pole pericycle cells supports their proposed role as serving as undifferentiated stem-cell reservoirs.