Spatio-Temporal Dynamics of the Patterning of Arabidopsis Flower Meristem

Abstract

The qualitative model presented in this work recovers the onset of the four fields that correspond to those of each floral organ whorl of Arabidopsis flower, suggesting a mechanism for the generation of the positional information required for the differential expression of the A, B, and C identity genes according to the ABC model for organ determination during early stages of flower development. Our model integrates a previous model for the emergence of WUS pattern in the floral meristem, and shows that this pre-pattern is a necessary but not sufficient condition for the posterior information of the four fields predicted by the ABC model. Furthermore, our model predicts that LFY diffusion along the L1 layer of cells is not a necessary condition for the patterning of the floral meristem.

Keywords: ABC model of flower development; WUSCHEL pre-pattern; gene regulatory networks; nonlinear dynamics of flowering; reaction-diffussion models.

FIGURE 1

ABC model of flowering. (a) ABC model of flowering for Arabidopsis. In this figure se: sepals; p: petals; s: stamen; and c: carpel. (b) Network representation of the interaction between the proteins LFY, AP1, TFL1, AG, and WUS. In this Figure (+) represents activation and (-) represents inhibition.

FIGURE 2

Emergence of the ABC zones of flower organ determination. (A) WUS pre-pattern is the result of the action of the inhibitory signal L from the extremes of the SAM L1 sheet that induces the activation of the inhibitory chemical signal y that restricts WUS expression to the inner whorl of the floral meristem. In the model we represent the floral meristem as a linear array of 15 cells that crosses the diameter of the four whorls. (B) Initial homogeneous spatial distribution of the chemical fields at the beginning of the simulation, LFY (red line), TFL1 (yellow line), AP1 (brown line) AG (black line), and WUS (blue line); (C) WUS pattern (blue line) arises at the center of the floral meristem after ∼1 h; and (D) the initial homogenous state of the floral meristem is completely broken after ∼16 h. AG is expressed at the center of the meristem (black line) and its presence moves AP1 away from this zone. In consequence, the floral meristem has been patterned into three well defined zones of gene expression. In all Figures ε = 5. In all panels L(1) = L(2) = L(3) = L(13) = L(14) = L(15) = 1, and L(j) = 0 for 4 ≤ j ≤ 12; in similar form: y(1) = y(2) = y(3) = y(13) = y(14) = y (15) = 1, and y(j) = 0 for 4 ≤ j ≤ 12.

FIGURE 3

Effect of the spatial extent of the inhibitory signals L and y. In this Figure L = 1 and y = 1 for cells 1 and 15; L = 0 and y = 0 otherwise. The effect of decrease the spatial extent of the inhibitory signals L and y is to pattern the floral meristem into a spatio-temporal stable dissipative structure, which becomes broader and asymmetric with respect to cell 8 and resembles an altered floral structure. In this Figure t = 16 h and ε = 5.