Unraveling the Potential UV-B Induced Gene Expression of the Primary and Secondary Metabolisms Against Environmental Stress in Shallot

Development of climate-resilient crops is adopted to cope with environmental stress. Activation of plant protective genes through radiation of ultraviolet-B (UV-B) has attracted more concerns in contributing to abiotic and biotic stress prevention. Plants exposed to a certain dose of UV-B irradiation give specific responses in growth and metabolite biosynthesis patterns. It has been interpreted that these responses in accumulation of primary and secondary metabolites improve plant tolerance to abiotic and biotic stresses. The potential use of UV-B light as a tool to enhance plant defense systems in agricultural practice has gained increasing interest. In terms of shallot as a plant model in this study, each cultivar exhibits complex responses to UV-B exposure at the transcription level of gene expression. The metabolic pathways in plants after UV-B exposure followed by abiotic and biotic stress are still unclear and necessary to be explored. This review provides a preliminary study of current understanding on UV-B-induced response and protective mechanism in shallot, particularly focusing on modulation of primary and secondary metabolic processes involved in pathogen and drought stress responses. In the primary metabolism, low intensity of UV-B exposure increases the sucrose phosphate synthase (SPS) expression in shallot Tuktuk cultivar. While in the secondary metabolic process, the expression level of lypoxigenase-2 (LOX-2) and cinnamyl alcohol dehydrogenase (CAD) are upregulated differently in two Indonesia shallot cultivars, Lokananta and Tuktuk. Upon the UV-B exposure to various types of stressors, such as Fusarium acutatum pathogen inoculation, the expression of LOX-2 is found to be upregulated in most of the exposures to resist the stress situation encountered. On the other hand, the expression of phenylalanine ammonia lyase (PAL) and chalcone synthase-A (CHS-A) are also upregulated through UV-B exposure followed by in vitro drought stress simulation. The gene encoding the secondary metabolites production, including the phenylpropanoid pathway products, is important to induce the protective mechanism in plant system. This mechanism assumes that UV-B plays a specific role as a prior exposure whereby a stimulus potentiates the defense mechanism. UV-B priming triggers biotic and abiotic tolerance by acting as warning signals at the transcription to phenotype levels. © 2024, Gifu University - United Graduate School of Agricultural Science. All rights reserved.