From diffuse growth to planar polarity in Arabidopsis root epidermal cells

Plant roots fulfill important functions as they serve in water and nutrient uptake, provide anchorage of the plant body in the soil and in some species form the site of symbiotic interactions with soil-living biota. Root hairs, tubular-shaped outgrowths of specific epidermal cells, significantly increase the root's surface area and aid in these processes. In this review we focus on the molecular mechanisms that determine the hair and non-hair cell fate of epidermal cells and that define the site on the epidermal cell where the root hair will be initiated (= planar polarity determination). In the model plant Arabidopsis, trichoblast and atrichoblast cell fate results from intra- and intercellular position-dependent signaling and from complex feedback loops that ultimately regulate GL2 expressing and non-expressing cells. When epidermal cells reach the end of the root expansion zone, root hair promoting transcription factors dictate the establishment of polarity within epidermal cells followed by the selection of the root hair initiation site at the more basal part of the trichoblast. Molecular players in the abovementioned processes as well as the role of phytohormones are discussed, and open areas for future experiments are identified

Microscale Thermophoresis (MST) to Study Rapid Alkalinization Factor (RALF)-Receptor Interactions

Abstract: Microscale thermophoresis (MST) is a simple but powerful tool to study the in vitro interaction among biomolecules, and to quantify binding affinities. MST curves describe the change in the fluorescence level of a fluorescent target as a result of an IR-laser-induced temperature change. The degree and nature of the change in fluorescence signal depends on the size, charge, and solvation shell of the molecules, properties that change in function of the binding of a ligand to the fluorescent target. We used MST to describe the interaction between components of a regulatory module involved in plant cell wall integrity control. This module comprises the secreted peptide Rapid Alkalinization Factor 23 (RALF23) and its receptor complex consisting of the GPI-anchored receptor Lorelei-Like Glycoprotein 1 (LLG1) and a receptor kinase of the CrRLK1L family, FERONIA. Here we show how MST can also be used to study three-partner interactions