Stem Cell Activity and Regeneration In Roots Require Non-Cell Autonomous Regulation From The Ground Tissue

Stem cells are central to plant development. Root stem cells organize around the quiescent center (QC) and give rise to cell lineages that generate the root radial pattern during postembryonic development. Here, through analyses of mutants in the transcription factors BLUEJAY, JACKDAW and SCARECROW and chemical treatments, we have found that QC regenerative capacities maintain the stem cell niche during postembryonic development; and in addition, specification of QC cells are required to re-establish the radial pattern upon wounding. Our data shows that QC functionality in maintaining and regenerating the radial pattern requires non-cell-autonomous regulation by transcription factors BLUEJAY, JACKDAW and SCARECROW. We observe that these factors regulate auxin transport, auxin maxima formation, as well as the stem cell regulator SHORT-ROOT from the ground tissue. We tracked this non-cell-autonomous regulation to C-REPEAT BINDING FACTOR 3 (CBF3). CBF3 protein is mobile, while gene is expressed in the ground tissue downstream of BLUEJAY, JACKDAW and SCARECROW. Targeted-expression of to the ground tissue of mutant recovers radial patterning and, upon laser ablation, stem cell niche regeneration and tissue organization in layers. CBF3 also regulates QC organization and inhibits stem cell niche differentiation. We propose CBF3 may function as a radial signal maintaining stem cell niche activity and regeneration.