The amazing regenerative plasticity of plants. How is a new organ regenerated after embryogenesis?

Plants have striking regeneration capacities, and can produce new organs from postembryonic tissues. Aerial explants (stems or leaves) can regenerate roots leading to formation of functional plants and survival. This process is known as rooting and has great biotechnological potential such as generation of plants resistant to disease, plant breeding and micro-propagation. Rooting can be induced by stress, wound or hormone supplementation, usually auxins. Rooting in in vitro culture is normally induced by hormone application, although it can also be achieved in hormone-free medium facilitating manipulation. The molecular mechanisms involved in hormone-free rooting remain largely unexplored.

Research carried out at the CBGP by the laboratory of "ROOT ORGANOGENESIS, REGENERATION AND ROOTING" in collaboration with researchers from the University of Elche, has identified the morphological events and main molecular regulators involved in hormone-free rooting in the model plant Arabidopsis thaliana. This research has been published in Plant Physiology.

Regeneration of new functional roots takes about 6-7 days. Regeneration begins with the activation of auxin and cytokinin biosynthesis genes, as well as of auxin transporters, resulting in confluent local hormonal signaling in the area adjacent to the excision point (Fig.1A). This signaling triggers vasculature-cell proliferation leading to formation of a callus like structure which is required for leaf rooting. We have named this structure endogenous callus, as it is different from hormone-induced callus. Subsequently, cell reprogramming is required, and thus we have identified genes and factors involved in specification of root founder cells and stem cells. These factors also regulate tissue formation and patterning of the new root (Fig.1B).