Chapter 19 - Crosstalk of hormones, second messengers, and MAPK in plant defense

Abstract

Hormones such as auxin, abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), ethylene (ET), brassinosteroids , and gibberellins are known to provide plant resistance against both biotic and abiotic stresses and mediate their action through mitogen-activated protein kinase (MAPK) cascades. In addition to their role in plant growth and development, JAs and SAs participate in systemic acquired response and wounding and provide plant resistance toward external damages caused by herbivores, insects, pathogens, mechanical injury, etc., by inducing resistance gene expression. ABA is known to have remarkable impacts on plant defense against pathogens like bacteria, fungi, and viruses. Polyhydroxy steroid hormone brassinosteroid, melatonin, and some other phytohormones mediate plant defense by increasing antioxidant enzymes and producing secondary messengers like reactive oxygen species, and nitric oxide. During plant–pathogen interaction, dynamic alterations in the cytosolic calcium ion levels lead to the activation of plant-triggered immunity through MAPK. The gaseous plant stress hormone, ET, is known to act on several genes involved in the plant defense pathway. The pathways of the phytohormones are connected to each other in a complex and unknown network. Auxin is known to act antagonistically with SA during plant defense while shares commonalities with JA signaling pathway. This chapter highlights the crosstalks that take place between the hormones and the second messengers and are executed by the MAPK pathway to confer plant resistance to biotic and abiotic stress.