Mechanosensitive control of plant growth: bearing the load, sensing, transducing, and responding

Abstract

As land plants grow and develop, they encounter complex mechanical challenges, especially from winds and turgor pressure. Mechanosensitive control over growth and morphogenesis is an adaptive trait, reducing the risks of breakage or explosion. This control has been mostly studied through experiments with artificial mechanical loads, often focusing on cellular or molecular mechanotransduction pathway. However, some important aspects of mechanosensing are often neglected. (i) What are the mechanical characteristics of different loads and how are loads distributed within different organs? (ii) What is the relevant mechanical stimulus in the cell? Is it stress, strain, or energy? (iii) How do mechanosensing cells signal to meristematic cells? Without answers to these questions we cannot make progress analyzing the mechanobiological effects of plant size, plant shape, tissue distribution and stiffness, or the magnitude of stimuli. This situation is rapidly changing however, as systems mechanobiology is being developed, using specific biomechanical and/or mechanobiological models. These models are instrumental in comparing loads and responses between experiments and make it possible to quantitatively test biological hypotheses describing the mechanotransduction networks. This review is designed for a general plant science audience and aims to help biologists master the models they need for mechanobiological studies. Analysis and modeling is broken down into four steps looking at how the structure bears the load, how the distributed load is sensed, how the mechanical signal is transduced, and then how the plant responds through growth. Throughout, two examples of adaptive responses are used to illustrate this approach: the thigmorphogenetic syndrome of plant shoots bending and the mechanosensitive control of shoot apical meristem (SAM) morphogenesis. Overall this should provide a generic understanding of systems mechanobiology at work.

Epidermal bladder cells confer salinity stress tolerance in the halophyte quinoa and Atriplex species

“…The physiological role of EBC in plant adaptive responses to salinity has been a matter of numerous experimental and review papers (see the Introduction section), but the reported evidence is mostly circumstantial. Here we show that the gentle removal of EBC, which did not cause any thigmomorphogenic response (Kamano et al 2015;Moulia et al 2015), results in a salt-sensitive phenotype. This provides the first direct evidence for a role of EBC in salt tolerance in halophytes.…”

“…; Moulia et al . ), results in a salt‐sensitive phenotype. This provides the first direct evidence for a role of EBC in salt tolerance in halophytes.…”

Forest trees filter chronic wind‐signals to acclimate to high winds

“…However, the strains (= the sensed stimuli) were not quantified and the time resolution was too low to give insights into the processes by which thigmomorphogenesis takes place. From data on isolated cells, Moulia et al (2011Moulia et al ( , 2015 have suggested the existence of sensing thresholds but they did not measure them in whole-plant experiments. We may speculate that these thresholds could be tuned to the prevailing chronic loads.…”

The RNA Polymerase-Associated Factor 1 Complex Is Required for Plant Touch Responses

“…The mechanical stimulus received by cells in the rosette leaves of plants that have been touched, sprayed, blown or bent must be transmitted to the cells of the shoot apical meristem in order to control elongation of the future shoot or stem (Moulia et al , 2015). …”