In vivo measurement of the Young's modulus of the cell wall of single root hairs.

Root hairs are cells from the root epidermis that grow as long tubular bulges perpendicular to the root. They can grow in a variety of mechanical or chemical environments. Their mechanical properties are mainly due to their stiff cell wall which also constitutes a physical barrier between the cell and its environment. Thus, it is essential to be able to quantify the cell wall mechanical properties and their adaptation to environmental cues. Here, we present a technique we developed to measure the Young's (elastic) modulus of the root hair cell wall. In essence, using custom-made glass microplates as cantilevers of calibrated stiffness, we are able to measure the force necessary to bend a single living root hair. From these experiments one can determine the stiffness and Young's modulus of the root hair cell wall.

A Microfluidic-Like System (MLS) to Grow, Image, and Quantitatively Characterize Rigidity Sensing by Plant's Roots and Root Hair Cells.

Plant's roots grow in soils of different rigidities. Understanding how the stiffness of the surrounding environment impacts growth and cell fate of roots and root hair cells is an important and open question. Here, we describe a simple method to setup a microfluidic-like system (MLS) to tackle this question. This system enables to grow plantlets during weeks in microfluidic chips filled with gels of controlled stiffness and to image them under a microscope from a few minutes up to a few days. Furthermore, MLS keeps the numerous benefits of microfluidic chips, such as high-resolution imaging, precise control of the geometry of growth, and standardization of the measurements. In sum, MLS enables one to quantitatively test, even on long time scales, the effect of the rigidity and the geometry of the environment on the growth of roots and root hair cells, including mechanotransduction to the nucleus.

RNA diversification by a self-reproducing ribozyme revealed by deep sequencing and kinetic modelling.

We demonstrate that a recombinase ribozyme achieves multiple functions in the same reaction network: self-reproduction, iterative elongation and circularization of other RNAs, leading to synthesis of diverse products predicted by a kinetic model. This shows that key mechanisms can be integrated and controlled toward Darwinian evolution in RNA reaction networks.