Phytohormone-Mediated Regulation of Heat Stress Response in Plants

Heat stress is one of the most devastating abiotic stresses that cause substantial yield loss around the world. Heat stress induces excessive production of reactive oxygen species, which negatively affect lipids, proteins and nucleic acids in plants. Protective mechanisms are tightly driven by phytohormones, the key molecules regulating plant growth, development and interactions with the environment. Hormonal cross-talk among abscisic acid, salicylic acid, jasmonic acid, ethylene, auxins, cytokinins, gibberellins, brassinosteroids, strigolactones and karrikins may promote stress tolerance, thermomorphogenesis as well as early senescence. Phytohormone synthesis and signalling are affected by temperature sensors and vice versa; they can influence production and function of the sensors. This chapter also summarizes plant sensing and signalling of high temperatures by calcium ions, hydrogen peroxide, reactive oxygen species, membrane lipids, phytochrome B, histone modifications, DNA remodelling, RNA stability and alternative splicing, methyl erythritol cyclodiphosphate (MEcPP), volatile compounds and changes in photosynthesis. The central regulatory role of phytochrome interacting factor 4 (PIF4), H2O2 and heat shock proteins (HSPs) is highlighted. Detail knowledge about molecular mechanisms is described in the relation to warm stress, heat shock, stress acclimation and stress memory. Organ-specific responses uncovered the key protective mechanisms in meristematic tissues and roots, which are driven by phytohormones. At the subcellular level, not only chloroplasts and mitochondria are involved in heat stress responses, but also endoplasmic reticulum and processes on plasma membrane are crucial for stress signalling. The unique scheme of heat-induced interactions among phytohormones is presented in this chapter. Possible ways of future research are suggested.