THE COLD-INDUCED FACTOR CBF3 MEDIATES ROOT STEM CELL ACTIVITY, REGENERATION AND DEVELOPMENTAL RESPONSES TO COLD

Plant growth and development involves the specification and regeneration of stem cell niches (SCNs). Although plants are exposed to disparate environmental conditions, how environmental cues affect developmental programs and stem cells is not well understood. Root stem cells are accommodated in meristems in SCNs around the quiescent center (QC), which maintains their activity. Using a combination of genetics and confocal microscopy to trace morphological defects and correlate them with changes in gene expression and protein levels, we show that the cold-induced transcription factor (TF) C-REPEAT BINDING FACTOR 3 (CBF3), which has been previously associated to cold acclimation, regulates root development, stem cell activity and regeneration. CBF3 is integrated into the SHORT-ROOT (SHR) regulatory network forming a feedback loop that maintains SHR expression. CBF3 is primarily expressed in the root endodermis, while CBF3 protein is localized to other meristematic tissues including root SCNs. Complementation experiments of cbf3-1 using a wild-type CBF3 gene and a CBF3 fusion with reduced mobility, show that CBF3 movement capacity is required for SCN patterning and regulates root growth. Notably, cold induces CBF3 affecting QC activity. Furthermore, exposure to moderate cold around 10-12 °C promotes root regeneration and QC re-specification in a CBF3 dependent-manner during the recuperation period. In contrast, CBF3 does not appear to regulate stem cell survival, which has been associated to recuperation from more acute cold (∼4 °C). We propose a role for CBF3 mediating the molecular interrelationship between the cold response, stem cell activity and development.