Abstract
Regulated auxin patterning provides a key mechanism for controlling root growth and development. We have developed a data-driven mechanistic model using realistic root geometry and formulated a principle to theoretically investigate quantitative auxin pattern recovery following auxin transport perturbation. This principle reveals that auxin patterning is potentially controlled by multiple combinations of interlinked levels and localisation of influx and efflux carriers. We demonstrate that (1) when efflux carriers maintain polarity but change levels, maintaining the same auxin pattern requires non-uniform and polar distribution of influx carriers; (2) the emergence of the same auxin pattern, from different levels of influx carriers with the same nonpolar localisation, requires simultaneous modulation of efflux carrier level and polarity; and (3) multiple patterns of influx and efflux carriers for maintaining an auxin pattern do not have spatially proportional correlation. This reveals that auxin pattern formation requires coordination between influx and efflux carriers. We further show that the model makes various predictions that can be experimentally validated.
Highlights
Our model integrates the following experimental data: (1) a root structure with cell geometries derived from confocal microscopy imaging[13], where each cell has a cytosolic space, plasma membrane and cell wall; (2) PIN and AUX1/LAX carrier localisation based on experimental images[11,13,17,18,19,20]; (3) PIN polarity; and (4) experimental data describing hormonal crosstalk between efflux carriers (PIN1 and PIN2) and hormones[21]
We formulate a general principle for quantitative auxin pattern recovery which demonstrates how relationships between influx and efflux carrier level and localisation can possibly combine to quantitatively control auxin patterning and the emergence of specific auxin patterns, which demonstrates that the relationship between influx and efflux carriers, not their individual activity, regulates auxin patterning
Experimental evidence shows that the quantitative properties of auxin gradients are important factors in regulating Arabidopsis root development
Summary
Answers will determine how influx and efflux carrier levels and localisation combine to control auxin pattern formation and clarify the individual roles of polar PIN and nonpolar AUX1/LAX carriers in maintaining auxin patterning. This study seeks answers through data-driven mechanistic modelling analysis, in which we explicitly include the polar PIN and nonpolar AUX1/LAX carriers. We formulate a general principle for quantitative auxin pattern recovery which demonstrates how relationships between influx and efflux carrier level and localisation can possibly combine to quantitatively control auxin patterning and the emergence of specific auxin patterns, which demonstrates that the relationship between influx and efflux carriers, not their individual activity, regulates auxin patterning. We show that our model makes various predictions that can be validated experimentally
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