Fig. 1: Root stem cells and early derivatives develop long G1 under control of the RBR1 pathway.
From: Stem cell regulators drive a G1 duration gradient during plant root development
a, Top: a root tip of the three-colour cell cycle marker line PlaCCI showing nuclei in G1 (cyan), S + early G2 (red) and late G2 + M (yellow). The image includes the RAM at the tip, followed by the elongation zone in the upper part of the root. Bottom: enlarged view of the white square in the top image, focusing on the QC, the stem cell niche and the surrounding early derivatives. The epidermal (epi) layer, which contains atrichoblasts and trichoblasts that will give rise to non-hair and hair cells, respectively, in the differentiated part of the root; cortical (cor) layer; and endodermal (endo) layer are indicated. The position of the QC is set as 0.0 and the RAM boundary as 1.0 in this and subsequent figures. This is a representative image of more than ten different roots imaged. Scale bars, 20 µm. WT, wild type. b, Live-imaging example showing an epidermal cell (trichoblast), located at position 0.76 of the RAM, in metaphase (0 min). After division, the two daughter cells load CDT1a (cyan). Since CDT1a is rapidly degraded at the G1/S transition (vertical white arrows), it is a proxy of G1 duration. Scale bar, 10 µm. c, G1 duration in four root cell types (atrichoblasts, trichoblasts, cortex and endodermis), as indicated, along the RAM. The position of the QC is set as 0.0 and the RAM boundary as 1.0. The data points correspond to the G1 duration of individual cells quantified from different recorded videos (up to 20 h long using confocal microscopy). The numbers of cells recorded were 37, 46, 68 and 76 for atrichoblasts, trichoblasts, cortex and endodermis, respectively, taken from five roots. d, Live imaging of cells showing the period from metaphase/anaphase until the initiation of CDT1a loading. Examples of a short (top) and a long (bottom) period of CDT1a loading initiation (black lines) are shown. Scale bars, 10 µm. e, Quantification of CDT1a loading time (between metaphase/anaphase and the first detectable CDT1a signal) along the RAM in four cell types, as indicated. Total n = 128 cells from four roots. f, Left: root tip of the rbr1 loss-of-function mutant (rRBr) expressing the PlaCCI markers. Scale bar, 20 µm. Right: G1 duration in four root cell types (atrichoblasts, trichoblasts, cortex and endodermis; n = 62, 44, 94 and 95, respectively, taken from nine roots), as indicated by the colour code, along the RAM in the rRBr mutant. The shaded shape covers all data points of G1 < 20 h shown in c.
