Date: 14th December 2022
Title: Reverse engineering the earliest stages of lateral root formation
Location: Lecture room B5, Forest Sciences Building, Latokartanonkaari 7-9 and remotely via Zoom
Host: Ari-Pekka Mähönen
Abstract: Root system architecture determines a plants access to water and nutrients, and is thus a major determinant of plant fitness. Still, the earliest steps in lateral root formation, priming and prebranch site formation, are thusfar poorly understood. In Arabidopsis, lateral root priming involves semi-regular oscillations in auxin levels and/or signalling, accompanied by waves of gene expression. Through growth these temporal oscillations become translated into a spatially periodic pattern of primed cells along the axis of the main root.
Using a multi-scale modeling approach, we recently demonstrated that priming may emerge automatically from the interplay between realistic, stem cell driven root tip growth dynamics and auxin transport. Specifically, we show that stem cell driven growth results in period alterations in cell size and thereby auxin uptake capacity, while the root tip reflux loop results in an auxin loading zone at the start of the elongation zone. Combined this results in oscillations in auxin level. By comparing predictions from our model and earlier proposed mechanisms for priming against experimental data we were able to validate this mechanism.
Still, in our model and experimental data, auxin levels initially decline after priming, raising the question how auxin signalling levels are secondarily elevated in primed cells to result in stable prebranch site formation. Our model suggests that this secondary increase and subsequent maintenance of auxin signalling requires a increase in auxin signalling capacity through upregulation of ARFs specifically in primed cells. These results offer a reconciliation of the debate on whether oscillations in auxin itself or rather in auxin signalling capacity drive early lateral root formation.
Kirsten ten Tusscher is a professor in Computational Developmental Biology. Her research focuses on the development and use of state-of-the art multi-scale simulation models to decipher the patterning processes underlying development in multicellular organisms, with in recent years a predominant focus on plant root and vasculature patterning. A key aspect of her work is to investigate how the bidrectional interplay between patterning and growth processes shapes self-organized growth, development and regeneration of plant roots. Additionally, a major focus in the lab is to decipher how plants sense, process and integrate environmental information to decide on where the invest in growth and in which directions to grow. Examples are the directional growing away of plant roots from salt gradients and the preferential foraging of plant roots in nutrient rich patches.