Stem Cell Niche Regeneration After Symplastic Isolation In Arabidopsis Roots

The stem cell niches(SCN)plays important roles in root growth.The quiescent center(QC)cells located in the center of the stem cell niches and fuction to maintain the stemness in the surrounding stem cells.When QC and surrounding stem cells was blocked,SCN entirely lost the stemness.Using this system,we examined how QC and SCN were regenerated after the symplastic communication was restored.First we found that the degradation of callose was fast after removal of ES tradiol inducer,allowing recovery of the symplastic communication within SCN.By observing phenotypic changes of pWOX5:erGFP and other reporter maker lines,we found that morphological QC formation was earlier than functional QC during the regeneration.By observing the changes of tissue-specific genes,we found the division frequency of different parts of root tip changed over time.In early period of regeneration,auxin enrichment in vascular stem cells resulted in relatively strongerdivision.In the later stage,this division frequency gradually became weaker,and the division peak shifted to endodermis cells.This caused the distinct contribution of different tissues during the SCN reestablishment.By observing the changes of the relative distribution of auxin and cytokinin in the same root,we found that the distribution of auxin was reduced in the SCN firstly,and then slowly extended to the root cap,while cytokinin seemed to gradually decrease in the site where auxin appeared.This exclusive pattern indicated a mutual antagonistic effect between these two hormone during the regeneration.However,during the recovery,the distribution of auxin gradually returned to the normal pattern and both cytokinin and auxin slowly overlapped,indicating the different interactions between auxin and cytokinin during the recovery of new SCN.Our study provides a direct live observations of SCN regeneration in an intact Arabidopsis root.