“…To explore the degree of regulatory conservation in angiosperm root development, we profiled chromatin accessibility in 4,655 nuclei from 7-day old embryonic root tissues in the eudicot model species A. thaliana, integrated with previously generated A. thaliana root scRNAseq data (n=12,606), and constructed eight cis-regulatory pseudotime trajectories encompassing vascular, dermal and ground development (Figure7A-7C, S11 and S12A; TableS13-S17).Maintaining focus on PCC development, we first validated the utility of the integrated data sets by visualizing gene expression and accessibility of known marker genes representative of QC (WUSCHEL-RELATED HOMEOBOX 5, WOX5), procambial (WUSCHEL-RELATED HOMEOBOX 4, WOX4) and PCC (SUCROSE TRANSPORTER 2, SUC2) cell types (Figure7Dand 7E). Next, we aligned Z. mays and A. thaliana PCC trajectories using a time-warping algorithm to enable direct comparison of gene accessibility dynamics in a common space.Consistent with recent comparative analysis of vascular development in O. sativa, A. thaliana, and Solanum lycopersicum(Kajala et al, 2020), only 206 out of 10,976 putative orthologs were significantly associated (FDR < 0.01) with PCC pseudotime in both species, indicating that the majority PCC trajectories-associated genes are unique to each lineage (97% Z. mays, 83% A.thaliana). However, of the 206 PCC-associated orthologs, ~50% (102/206) exhibited similar patterns of gene accessibility across pseudotime (Figure 7F, 7G, S12B).…”