The (un)likelihood of clock-driven lateral root priming; A modeling exploration

Abstract

Lateral root formation starts with priming, predisposing subsets of pericycle cells with the potential of future lateral root formation through semi-periodic elevations in auxin (signalling). While various mechanisms have been suggested, the most broadly accepted hypothesis proposes a genetic, cell-autonomous root clock akin to the clock underlying vertebrate somitogenesis. Still, while gene expression variations were observed, so far this clock has not been proven. From a functional and evolutionary perceptive it is furthermore an open question whether lateral root priming is not more likely to arise from an emergent tissue level process similar to phyllotaxis. To help settle this debate in this study I use general knowledge of oscillator dynamics and simple models of auxin signalling to underline the unlikelihood of a root clock driving lateral root priming. I show how within a single cell oscillations are limited to a small parameter domain, with constraints intensifying due to the presence of multiple AUX/IAA and ARF types. Furthermore, I demonstrate how non-meristem based oscillations, due to a lack of memory of oscillator phase, can not drive periodic prebranch site formation.