Fig. 3: The KRP5–RBR1 pathway controls G1 duration and links with the PLT root patterning genes.
From: Stem cell regulators drive a G1 duration gradient during plant root development
a, KRP5 expression depends on PLT2. Left: root tips of plants expressing the KRP5–GFP translational fusion expressed under the KRP5 promoter in the wild type, 35S::PLT2-GR after 22 h of Dex treatment and plt1,plt2. Scale bars, 20 µm. Right: quantification of the KRP5–GFP signal along the RAM (control WT, n = 472 cells, four roots; 35S::PLT2-GR, n = 818 cells, four roots; plt1,plt2, n = 183 cells, five roots) along the RAM (0 is the QC; 1.0 is the RAM boundary). b, Left: root tip of a krp5-1 mutant expressing the PlaCCI markers. Scale bar, 20 µm. Right: G1 duration in four root cell types (atrichoblasts, trichoblasts, cortex and endodermis; n = 78, 73, 68 and 59, respectively, from six roots), as indicated, along the RAM. The shaded shape is taken from Fig. 1f and is included here to facilitate comparison with the values of G1 duration in the wild type. c, Transcript levels of all KRP genes were analysed by reverse transcription–quantitative polymerase chain reaction (RT–qPCR) in four-day-old roots of 35S::PLT2-GR plants before (−Dex, control) and after (+Dex) Dex treatment (1 h and 3 h). The expression data were normalized to GAPC-2 (AT1G13440). The bars represent the mean ± s.d. from three (+Dex 3 h) or four (−Dex and +Dex 1 h) biological replicates, and the individual points indicate the mean of three technical replicates for each biological replicate. Statistically significant differences were determined by a two-way analysis of variance followed by two-sided Tukey’s multiple comparison tests: **P < 0.01; ***P < 0.001; ****P < 0.0001. Note that the other statistically non-significant comparisons (P > 0.05) have been omitted for simplicity. d, Left: root tip of a krp1,2,3,4,5,7 mutant expressing the PlaCCI markers. Scale bar, 20 µm. Right: G1 duration in four root cell types (atrichoblasts, trichoblasts, cortex and endodermis; n = 51, 45, 69 and 99, respectively, from two roots), as indicated, along the RAM. The shaded shape is taken from Fig. 1f and is included here to facilitate comparison with the values of G1 duration in the wild type. e, Basic components of the IFFL identified in this study that controls the developmental regulation of G1 duration in the RAM. PLT proteins that show a proximal–distal gradient in the RAM play opposing functions: they confer cell proliferation potential and also activate expression of the CDK inhibitor KRP5, which in turn restricts RBR1 phosphorylation and prolongs the G1 phase. f, Stimulation of cell division by PLT2 is restricted by KRP5. The 35S::PLT2-GR construct was expressed with and without Dex in the wild-type and krp5-1 mutant backgrounds, as indicated. Left: details of the epidermal layer in the different experimental conditions. Scale bars, 20 µm. Right: quantification of the amount of cortical cell divisions in the RAM before and after 3 h of Dex treatment. The bars represent mean ± s.d., and the data points correspond to individual roots of the following biological replicates: 35S::PLT2-GR −Dex (n = 9), 35S::PLT2-GR +Dex (n = 8), 35S::PLT2-GR,krp5-1 −Dex (n = 9) and 35S::PLT2-GR,krp5-1 +Dex (n = 10). Statistical significance between genotypes was determined using one-way analysis of variance followed by Tukey’s multiple comparison tests (two sided): **P < 0.01; ****P < 0.0001.
