Elucidating thigmomorphogenesis : an epigenetic phenomenon of mechanical stress acclimation in plants

Abstract

Climate change culminating in increased temperature, sea-level rise, flooding amidst strong winds and heavy rainfall cause mechanical stress (MS) that affects the habitat of several plant species. In response, plants activate a plethora of molecular and physiological processes that alter their architecture causing a phenomenon referred to as thigmomorphogenesis. Plants develop thicker stem, smaller leaves, reduced height and overall increased in tensile strength. These alterations facilitate forest trees to survive windthrows and mitigate subsequent stress. Plants can desensitise their molecular response to repetitive MS, as an adaptive mechanism to prevent unwanted thigmomorphogenesis. Plants may want to 'remember' MS since it is natural ubiquitous stress stimuli that occur daily, be it from insect feeding, high winds, animal stamping or heavy rainfall. For more than a century, in Japan and China, stamping on crops, as a form of MS has been used to harden crops against extreme weather changes, pathogens, insect herbivory and to increase yield, a practice known as 'mugifumi'. However, the molecular mechanisms involved in MS-induced morphological changes, phytohormone regulation and gene regulation that promote stress acclimation are unclear. In this thesis, I unraveled how MS regulates the cross-talk between Jasmonic acid (JA), salicylic acid (SA) and gibberellic acid (GA) to affect thigmomorphogenesis and plant immunity. I showed that epigenetic processes such as permissive histone lysine methylation, DNA methylation, and RNA dependent DNA methylation pathways can mediate thigmomorphogenesis. Understanding these mechanisms can help farmers adopt MS as a sustainable agricultural practice to harden crops in modern agricultural systems (glasshouses and in commercial farms) in light of changing climatic conditions and to reduce the effect of pesticides on the environment.

Date of Award	2020
Original language	English