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2019/03/04 ABRC Seminar

Speaker: Dr. Guido Grossmann (Group Leader, the Centre for Organismal Studies (COS) Heidelberg, Heidelberg University, Germany)
Topic: Cellular growth regulation in roots - how to adapt in a complex environment

In nature, plant roots grow in highly heterogeneous conditions, which requires both systemic and local response mechanisms to modulate cellular growth and adapt organ morphology. How environmental cues are integrated into growth regulation and how systemic communication and cell-autonomous responses are interlinked in this process, remain challenging questions in plant biology. To facilitate the investigation of root-environment interactions, we combine the use microfluidic lab-on-a-chip platforms with live-cell imaging of roots. Over the past years, we developed a series of microfluidic devices for on-chip root growth under precisely controlled conditions. Here, we present the dual-flow-RootChip, a microfluidic organ-on-a-chip platform for asymmetric perfusion of Arabidopsis roots to investigate root growth, development, and signaling under simulated environmental heterogeneity. Applications range from monitoring physiology and signaling (e.g. calcium sign.) under asymmetric conditions, tracing molecular uptake and selective drug treatments to local infection or colonization by fungi or bacteria.
Using the dual-flow-RootChip, we revealed cell-autonomous regulation of root hair growth upon differential availability of inorganic phosphate (Pi). Independent of the overall Pi status of the root, we found that hair cells can triple their growth rate within minutes, when extracellular Pi levels rise, pointing to a direct modulation of the tip growth machinery and resulting in hair growth that followed the nutrient gradient.
To understand the molecular mechanisms of growth regulation in root hairs, we further dissected the tip growth machinery and unveiled a phased assembly process during the early stages of hair emergence. The transition between different phases depends on timed regulation of Rho of plants (ROP) GTPases. We identified a novel candidate that acts upstream of ROPs, pre-forms a polar domain at the plasma membrane, and is necessary and
sufficient to recruit ROPs in order to trigger the initiation of tip growth.

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