Role of Jasmonic and Salicylic Acid Signaling in Plants Under UV-B Stress

Jasmonic acid (JA) and Salicylic acid (SA) are the essential plant hormones responsible for the plant's proper growth and development. These signaling molecules have a significant role in plants along with the regulation of defense-mechanisms locally and systemically under various biotic and abiotic stresses. Among abiotic stresses, ultraviolet-B (UV-B) radiation coming to the Earth's surface due to depletion of the stratospheric ozone layer is of serious concern to all living organisms. UV-B is an important factor, negatively influencing the growth and yield of plants on this Earth, ultimately posing a threat to food security. Therefore, understanding the signaling behavior of JA and SA under UV-B stress will be definitely beneficial for the maintenance of agricultural productivity worldwide. Plant responses related to morphological, biochemical, physiological, growth, and yield have been extensively studied under UV-B stress, although studies conducted with UV-B exposure and its impact on plant's endogenous JA and SA contents are limited. On the other hand, some studies have also explored the regulatory impact of exogenously supplied JA and SA to the plants. More accumulation of endogenous JA and SA contents has been observed under elevated UV-B exposure in plants. JA and SA play synergistic as well as antagonistic roles during the regulation of defense responses under various stresses. An inverse relationship between JA and SA arewell established underUV-B stress in pea, soybean, and mungbean cultivars. Increased JA content provided better plant resistance while increased SA level imposed higher oxidative stress to plants when exposed to elevated UV-B. Oxidative stress caused by the higher accumulation of SA is well correlated with its inhibitory impact on catalase and ascorbate peroxidase activity leading to more generation of Reactive oxygen species (ROS) under UV-B exposure. JA has an inhibitory effect on the accumulation of SA by the regulation of NAC transcription factors like ANAC019/055/072 whereMYC2 binds to the promoter regions of theseNACtranscription factors, which further inhibits ISOCHORISMATE SYNTHASE1 (ICS1) expression, which is responsible for initiating the expression of BSMT1 (BENZOIC ACID/SA CARBOXYL MEHYLTRANSFERASE 1) during SA biosynthesis. Therefore, the present chapter will focus on the effect of UV-B stress in plants with special emphasis on JA and SA signaling, their antagonistic and synergistic behavior in plant defense, and ROS interaction.