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Clonal analysis reveals gradual recruitment of lateral root founder cells and a link between root initiation and cambium formation in Arabidopsis thaliana

The pericycle gives rise to lateral roots (LRs) and lateral meristems (LMs; cambium and phellogen), however, a thorough clonal analysis of pericycle cell lineage has not been investigated. This study fills in this gap and addresses pericycle impact in LR and LM development. Heath-shock inducible DS1 transposition in 35S-DS1-H2B:YFP; HS-Ac seedlings results in production of YFP-labelled cell clones. These clones in pericycle cell derivatives were identified with a confocal microscopy and subjected to 3D reconstructions and analysis. Participation of pericycle founder cells (FC) in LR formation is more variable than previously considered. LR initiation was found most commonly involved the specification of just one FC in the longitudinal and one or two cells in transverse direction. After LR initiation, FCs continue to be recruited in both directions from pre-existing cells. Anticlinal divisions in the pericycle resulting in LMs start already in the young differentiation zone where only the protoxylem is differentiated. The clonal analysis demonstrated that pericycle cell activity related to LR formation is not separated in time and space from that related to LM formation and that LR FC recruitment is a gradual process. The analysis demonstrated that immediate pericycle progeny lack self-renewal capacity.