Figure 1.
(A) Schematic representation of the WUS-CLV dynamics with respect to the activator-inhibitor system. (B) (solid line, Equation (2a); n = 2.0) and
(dashed line, Equation (2b)) are constraint functions ranged between 0 and
. (C) Schematic representation of a spatially restricted SAM. While
is the threshold of the activator (blue line) for the CZ differentiation, Zs is the threshold of diffusible molecule z (red line) for the SAM differentiation. (D) The SAM is regulated by the interaction between WUS-CLV dynamics at the molecular level and CZ-PZ relationship at the tissue level. (E) The procedure of numerical calculations is divided into four steps (for details, see Materials and Methods).
Figure 2.
Stem cell proliferation modes.
(A) The proliferation mode clearly depends on parameters and
. (B–E) Pattern evolution of the reaction-diffusion system in relation to cell division is classified into four proliferation groups: the fluctuation mode (B), emergence mode (C), division mode (D), and elongation mode (E). See also Movies S1, S2, S3, S4 (B–E, respectively). The intensity of the blue indicates the activator concentration (B–E).
Figure 3.
SAM patterns generated by the model.
(A) The model generates different SAM patterns by varying (WUS-CLV dynamics) and
(the spatial restriction). Crosses indicate situations where no patterns are generated. (B–H) SAM patterns can be divided into six groups according to their structure and proliferation mode. See also Movies S5, S6, S7, S8, S9, S10, S11 (B–H, respectively). Blue and red indicate the activator concentration in the CZ and PZ, respectively. The green area indicates the OZ.
Figure 4.
Effect of WUS and CLV on SAM patterning.
(A) As increases or
decreases, the SAM pattern shifts sequentially from the fluctuation pattern (filled diamonds), to the homeostasis pattern (open circles), then to the dichotomous pattern (open squares), and finally to the fasciation pattern (filled circles). Crosses indicate situations where no patterns are generated, and filled square indicates the multiplication pattern by the division mode. (B) The SAM area in the homeostasis pattern expands as
increases or
decreases. The blue and red areas indicate the relative sizes of the CZ and PZ, respectively. (C) The effect of
and
on the SAM patterning is summarized schematically. The predictions of our model agree with many experimental results (for details, see text). The blue, red, and green areas indicate the CZ, PZ, and OZ, respectively.
Figure 5.
Expression patterns of the pWUS::GUS reporter construct.
Top view of the SAM in wild type Ler (A) and wus-1 (B) plants. Wild-type plants show strong β-glucuronidase (GUS) activity as a single spot at the center of the SAM (A, arrowhead). In contrast, wus-1 plants have an enlarged SAM with multiple foci of expression at very weak levels (B, arrowheads). Ten-day-old seedlings were stained with GUS overnight. The broken lines indicate the extent of the SAM. Scale bars, 10 µm.
Figure 6.
Numerical simulations for experiments affecting SAM patterning.
(A) Conditional knockdown of CLV3 causes a gradual expansion of the CZ area. (B–C) Ectopic expression of pCLV1::WUS (B) or pCLV1::CLV3 (C) causes clv-like and wus-like SAM morphologies, respectively. (D–E) CZ spots reform after ablation of the CZ cells. CZ foci reform as either a single (D) or two spots (E). (F) As a result of the incision through the meristem center, the two halves reorganize into two new meristems. See also Fig. S2A (B), S2B (C), and Movies S12, S13, S14, S15 (A, D, E and F, respectively). Blue and red indicate the activator concentration in the CZ and PZ, respectively. The green area indicates the OZ.
Figure 7.
SAM pattern essentially depends on the proliferation mode and stem cell containment strength. The proliferation mode can be sub-divided into four groups, depending on the molecular dynamics regulating the SAM, such as WUS-CLV dynamics of A. thaliana. On the other hand, stem cell containment is associated with the spatial restriction of the dynamics. The blue, red and green areas indicate the CZ, PZ and OZ, respectively.