Shoot regeneration in plants: how are the cells selected and what governs their journey to become a complete plant
Plants have a remarkable ability to rebuild new shoot and root systems, and give rise to fully grown plants from any part when cultured under optimum conditions. This ability has been long exploited for the propagation of endangered and agronomically important plants, and is now popularly known as tissue culture. Classic literature views plant tissue culture as propagation of new plants from callus.
Callus is an undifferentiated mass of cells, appearing, for instance, on wound sites or on plant parts in culture. For several decades now, the humankind has been inducing new shoots from callus via the process of de novo shoot regeneration. However, not all callus cells become shoot. Only a few cells of the callus called shoot progenitors are selected to become new shoots. How these cells selected and what governs their formation into a complete plant?
In a recent paper published in the journal Developmental Cell, Dr. Kalika Prasad’s group described a chain of events leading to the selection of progenitor cells during shoot regeneration. The team includes collaborators from Finland, the Netherlands, and Australia and the work was initiated at IISER Thiruvananthapuram, where Dr. Prasad was working prior to joining IISER Pune.
The team identified a regulatory module, where a shoot promoting factor triggers the localized expression of a cell wall loosening enzyme thereby generating mechanical heterogeneity (difference in mechanical stress between the neighbouring cells). This in turn activates the necessary cell polarity to create optimum build-up of plant growth hormone auxin to facilitate the re-building of complete shoot system.
A very important finding of the study is that the mere abundance of shoot stem cell regulator is not a predictor of shoot identity. Rather, it is the product of feedback loops between cell polarity and mechanical heterogeneity. “The actual selection of progenitors seems stochastic. Our study rules out the idea that there could be a blue-print behind plant cell fate decisions,” adds Dr. Kalika Prasad on the primary findings from this work.
Vijina Varapparambath, Mabel Maria Mathew, Anju Pallipurath Shanmukhan, Dhanya Radhakrishnan, Abdul Kareem, Shubham Verma, João Jacob Ramalho, Bejoy Manoj, Archana Rajan Vellandath, Mohammed Aiyaz, Raji Krishna Radha, Amit N Landge, Ari Pekka, Mähönen, Marcus. G. Heisler, Dolf Weijers, Kalika Prasad (2022). Mechanical conflict caused by a cell wall loosening enzyme activates de novo shoot regeneration. Developmental Cell DOI: https://doi.org/10.1016/j.devcel.2022.07.017