Exogenous Gibberellin Treatment Enhances Melatonin Synthesis for Melatonin-Enriched Rice Production.

Ok Jin Hwang,Kyoungwhan Back

doi:10.3390/biom12020198

Abstract

Melatonin production is induced by many abiotic and biotic stressors; it modulates the levels of many plant hormones and their signaling pathways. This study investigated the effects of plant hormones on melatonin synthesis. Melatonin synthesis in rice seedlings was significantly induced upon exogenous gibberellin 3 (GA3) treatment, while it was severely decreased by GA synthesis inhibitor paclobutrazol. In contrast, abscisic acid (ABA) strongly inhibited melatonin synthesis, whereas its inhibitor norflurazon (NF) induced melatonin synthesis. The observed GA-mediated increase in melatonin was closely associated with elevated expression levels of melatonin biosynthetic genes such as TDC3, T5H, and ASMT1; it was also associated with reduced expression levels of catabolic genes ASDAC and M2H. In a paddy field, the treatment of immature rice seeds with exogenous GA led to enhanced melatonin production in rice seeds; various transgenic rice plants downregulating a GA biosynthesis gene (GA3ox2) and a signaling gene (Gα) showed severely decreased melatonin levels, providing in vivo genetic evidence that GA has a positive effect on melatonin synthesis. This is the first study to report that GA is positively involved in melatonin synthesis in plants; GA treatment can be used to produce melatonin-rich seeds, vegetables, and fruits, which are beneficial for human health.

Highlights

Melatonin is an indole alkaloid commonly found in plants and animals
A recent study showed that melatonin acts as a signaling molecule in the regulation of starch synthesis during normal growth [4]; it functions in the regulation of molecular chaperones in response to heat stress [5]
As our initial study of the roles of plant hormones in melatonin synthesis, we focused on GA

Summary

Introduction

Melatonin is involved in normal growth and development, and defense responses against many biotic and abiotic stressors [1,2]. The protective effects of melatonin against multiple adverse environmental (e.g., biotic and abiotic) stresses are attributable to its potent antioxidant and regulatory activities, which induce a vast array of relevant genes [2,3]. A recent study showed that melatonin acts as a signaling molecule in the regulation of starch synthesis during normal growth [4]; it functions in the regulation of molecular chaperones in response to heat stress [5]. The involvement of melatonin in a diverse array of biological activities strongly suggests that, similar to animals, plants possess melatonin receptors [6]. Cand was recently proposed as a phytomelatonin receptor [7], its potential phytomelatonin receptor role is controversial [8]

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