Timing is key to turn root into shoot

Plant cells show remarkable plasticity. For example, lateral roots can be converted into shoots by supplementing the culture medium with cytokinin, which induces shoot fate. When properly controlled, this conversion does not involve callus formation, and so allows a detailed analysis of the processes directing the switch of organ identity. Using this system, Philippe Rech and colleagues (p. 1187) find that competence for root-to-shoot conversion is restricted to a narrow time window of lateral root development, coinciding with the stage at which the stem cell niche is formed in the new root. Furthermore, conversion can be reversed during this period – auxin treatment can switch the tissue back to a root – confirming that organ identity is not immediately fixed. Importantly, the authors provide evidence that root-to-shoot conversion does not occur via dedifferentiation, but rather via a direct transdifferentiation process. Transcriptome and methylome profiling provide insights into the gene expression and epigenetic changes occurring during conversion. This atypical mode of organogenesis may lead to novel methods for the vegetative multiplication of valuable plant cultivars.