Organ regeneration does not require a functional stem cell niche in plants

Stem cells are widely seen as the mechanism that permits organ regeneration in both plants and animals. In the plant root system, the stem cell niche has been assumed to be a local pattern organizer, required for both continuous post-embryonic growth and regeneration. New work in a root-tip regeneration system now shows that the root stem cell niche is in fact not necessary for pattern formation and re-establishment of cell identity, thus separating the functions of growth and repatterning. When the Arabidopsis root tip is cut off, taking with it the stem cell niche, the plant's remaining cells are able to regenerate all the major tissues that make up the root tip. This finding suggests that there are as yet unknown mechanisms that coordinate organogenesis independently of a central organizer. In the plant root system it is thought that the stem cell niche is a local pattern 'organizer' required for both continuous post-embryonic growth and regeneration. Here, the root stem cell niche is shown to be not necessary for pattern formation and re-establishment of cell identity, separating growth from re-patterning. Plants rely on the maintenance of stem cell niches at their apices for the continuous growth of roots and shoots. However, although the developmental plasticity of plant cells has been demonstrated1, it is not known whether the stem cell niche is required for organogenesis. Here we explore the capacity of a broad range of differentiating cells to regenerate an organ without the activity of a stem cell niche. Using a root-tip regeneration system in Arabidopsis thaliana to track the molecular and functional recovery of cell fates, we show that re-specification of lost cell identities begins within hours of excision and that the function of specialized cells is restored within one day. Critically, regeneration proceeds in plants with mutations that fail to maintain the stem cell niche. These results show that stem-cell-like properties that mediate complete organ regeneration are dispersed in plant meristems and are not restricted to niches, which nonetheless seem to be necessary for indeterminate growth. This regenerative reprogramming of an entire organ without transition to a stereotypical stem cell environment has intriguing parallels to recent reports of induced transdifferentiation of specific cell types in the adult organs of animals2,3.