Activation of the Jasmonate Biosynthesis Pathway in Roots in Drought Stress

Roots are the primary organs that first sense the soil environment. Plant growth and development are largely dependent on the plant root system, due to its crucial role in water and mineral uptake. Symbiotic microorganisms affect and improve the root response to stresses. Root endophytes and bacteria synthesize a wide array of plant-protecting chemicals, hormones, and compounds acting on hormone degradation. Since hormonal homeostasis is tightly regulated, the effects of abiotic factors may translate to specific molecular mechanisms though hormone cross-talk. Abiotic below-ground stresses are early signals affecting root growth regulation, resource acquisition, and root-shoot communication. Abiotic stresses elicit early signals that need to be transduced at distance to affect protection mechanisms, such as growth regulation, resource acquisition, synthesis of osmoprotectants, change in water potential, and regulation of stomatal closure, among others. The oxylipin family of signals represents one of the main mechanisms employed by plants. This family comprises fatty acid hydroperoxides, hydroxy-, keto- or oxo-fatty acids, volatile aldehydes, divinyl ethers, and jasmonic acid. Most of them are volatile compounds participating in several physiological processes, defense mechanisms, stress adaptation, and communication with other organisms. This chapter reports on new insights into the role of the activation of jasmonic acid biosynthesis during abiotic stresses in plant roots, and on the importance of earlier and stronger jasmonic acid induction as a trait conferring better drought tolerance in legume varieties able to cope with water stress.