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Plant Specialized Metabolism Regulated by Jasmonate Signaling
Abstract As sessile and autotrophic organisms, plants have evolved sophisticated pathways to produce a rich array of specialized metabolites, many of which are biologically active and function as defense substances in protecting plants from herbivores and pathogens. Upon stimuli, these structurally diverse small molecules may be synthesized or constitutively accumulated. Jasmonate acids (JAs) are the major defense phytohormone involved in transducing external signals (such as wounding) to activate defense reactions, including, in particular, the reprogramming of metabolic pathways that initiate and enhance the production of defense compounds against insect herbivores and pathogens. In this review, we summarize the progress of recent research on the control of specialized metabolic pathways in plants by JA signaling, with an emphasis on the molecular regulation of terpene and alkaloid biosynthesis. We also discuss the interplay between JA signaling and various signaling pathways during plant defense responses. These studies provide valuable data for breeding insect-proof crops and pave the way to engineering the production of valuable metabolites in future.
Fig. 1 Elicitors and effectors influence the core regulation module of JA-mediated defense response. Inductive signals, including DAMPs, HAMPs and MAMPs, are perceived by PRRs at the cell surface to trigger de novo JA biosynthesis. At the resting stage, JAZ proteins block JA signaling by binding to transcription factors including MYCs. JAZs directly recruit corepressors, such as TPL, partially through NINJA. TPL then recruits HDAs that repress JA-response genes through chromatin remodeling. In the presence of JA-Ile, JAZs interact with COI1 to form a coreceptor, which leads to ubiquitination and proteasome-dependent degradation of JAZs, resulting in de-repression of MYCs. By binding with MED25 and recruiting additional coactivators (e.g. HAC1), MYCs recruit RNA polymerase II to form a transcription preinitiation complex that transcripts JAresponsive genes. Since the degradation of JAZ is crucial for activating JA response, it is frequently targeted by effectors of diverse attackers. Pathogen effectors COR, HopZ1a and HopBB1 promote the degradation of JAZs, resulting in enhanced JA signaling and depressed SA signaling. Additionally, viral effector (2b protein and bC1) and whitefly-secreted salivary protein Bt56 repress JA singing pathway in favor of insect performance.
Fig. 2 The JA-mediated regulation of biosynthetic pathways of specialized metabolites in plants. Schematic diagram of the regulation of specialized metabolite biosynthesis by JA. The modulated pathways include the biosynthesis of GLSs, sesquiterpenes and anthocyanins in Arabidopsis thaliana , artemisininAin. annua, terpenoid indole alkaloid (TIA C. )roseus in , nicotine Nicotiana in species and tanshinones and phenolic acidsSin. miltiorrhiza . Unbroken lines indicate proven links, whereas broken lines represent hypothetical links. Black arrows indicate synergistic interactions and brown T-bars indicate counteractions.