The Course of Mechanical Stress: Types, Perception, and Plant Response

SIMPLE SUMMARY: Mechanical stress is a substantial natural environmental constraint for plants that is induced by dry compacted soils, intense rain and windstorms, changes in gravity, and obstacles. It is crucial to completely comprehend the precise mechanisms of plant response and adaptation to mechanical stresses as it has been demonstrated that their performance and growth rates are strongly impacted by these conditions. Over the past few decades, research in different fields (botany, biomechanics, genetics, biochemistry, imaging, etc.) has offered fragmentary insights into the mechanisms used by plants to counteract mechanical pressures. In an attempt to illustrate the complete picture, this review synthesizes current mechanical stress knowledge and research gaps on both above- and below-ground organs of annual and perennial plants, underlying similarity/differences and providing future recommendations. ABSTRACT: Mechanical stimuli, together with the corresponding plant perception mechanisms and the finely tuned thigmomorphogenetic response, has been of scientific and practical interest since the mid-17th century. As an emerging field, there are many challenges in the research of mechanical stress. Indeed, studies on different plant species (annual/perennial) and plant organs (stem/root) using different approaches (field, wet lab, and in silico/computational) have delivered insufficient findings that frequently impede the practical application of the acquired knowledge. Accordingly, the current work distils existing mechanical stress knowledge by bringing in side-by-side the research conducted on both stem and roots. First, the various types of mechanical stress encountered by plants are defined. Second, plant perception mechanisms are outlined. Finally, the different strategies employed by the plant stem and roots to counteract the perceived mechanical stresses are summarized, depicting the corresponding morphological, phytohormonal, and molecular characteristics. The comprehensive literature on both perennial (woody) and annual plants was reviewed, considering the potential benefits and drawbacks of the two plant types, which allowed us to highlight current gaps in knowledge as areas of interest for future research.