Effects of Light Quality and Phytochrome Form on Melatonin Biosynthesis in Rice

Abstract

Light is an important factor influencing melatonin synthesis in response to cadmium treatment in rice. However, the effects of light quality on, and the involvement of phytochrome light receptors in, melatonin production have not been explored. In this study, we used light-emitting diodes (LEDs) to investigate the effect of light wavelength on melatonin synthesis, and the role of phytochromes in light-dependent melatonin induction in rice. Upon cadmium treatment, peak melatonin production was observed under combined red and blue (R + B) light, followed by red (R) and blue light (B). However, both far-red (FR) LED light and dark treatment (D) failed to induce melatonin production. Similarly, rice seedlings grown under the R + B treatment showed the highest melatonin synthesis, followed by those grown under B and R. These findings were consistent with the results of our cadmium treatment experiment. To further confirm the effects of light quality on melatonin synthesis, we employed rice photoreceptor mutants lacking functional phytochrome genes. Melatonin induction was most inhibited in the phytochrome A mutant (phyA) followed by the phyB mutant under R + B treatment, whereas phyB produced the least amount of melatonin under R treatment. These results indicate that PhyB is an R light receptor. Expression analyses of genes involved in melatonin biosynthesis clearly demonstrated that tryptophan decarboxylase (TDC) played a key role in phytochrome-mediated melatonin induction when rice seedlings were challenged with cadmium.

Suppression of Rice Cryptochrome 1b Decreases Both Melatonin and Expression of Brassinosteroid Biosynthetic Genes Resulting in Salt Tolerance

“…For instance, phytochromes absorb red (600–700 nm) and far-red (700–750 nm) light as part of their biological functions, whereas phototropins and cryptochromes (CRY) sense ultraviolet A/blue light (390–500 nm). The first molecular genetic analysis of the possible involvement of photoreceptors in melatonin synthesis was recently reported, in which rice phytochrome mutants exhibited decreased melatonin synthesis compared to wild-type plants, confirming a previous report that melatonin synthesis requires light [ 33 ]. However, the possible involvement of CRY in melatonin biosynthesis in plants remains unclear [ 35 ].…”

“…In comparison, melatonin is not induced in rice with cadmium treatment upon exposure to far-red light and the dark. The role of light quality in melatonin synthesis was confirmed genetically, with rice phytochrome (red and far-red photoreceptors) mutants synthesizing less melatonin than the wild type, which implies that melatonin synthesis is light-dependent in plants [ 33 ]. Here, we tested whether the blue-light photoreceptor (CRY) is also involved in melatonin biosynthesis.…”

“…The pivotal gene responsible for melatonin induction under light is that encoding tryptophan decarboxylase (TDC), the first committed step enzyme in melatonin biosynthesis, which converts tryptophan into tryptamine. The optimal light for the maximum induction of melatonin was found to be a combination of red and blue light, rather than red or blue alone; far-red light is unable to induce melatonin in response to cadmium treatment in rice, indicating that melatonin synthesis is predominantly associated with photosynthesis rather than with other photoreceptors such as phytochromes [ 33 ].…”

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

“…Regulation of the synthesis and degradation of the evolutionarily conserved PSII D1 reaction center is mediated by post-translational RNA modulations [ 1118 , 1119 , 1120 ] and the presence of ATP [ 1121 ] in a light-dependent manner, where synthesis and/or degradation is induced by light but ceased in the dark. Unlike animals [ 1122 ], melatonin in plants is increased by the presence of light [ 1123 , 1124 ], and treatment with melatonin enhanced the synthesis of PSII D1 reaction centers in tomato seedlings under salt stress [ 1125 ]. Cyanobacteria, the only known prokaryote capable of water oxidation [ 431 ] which also produces melatonin [ 421 , 422 ], has recently been shown to exhibit circadian rhythm in the formation and dissolution of MLOs that remained soluble during daylight, but became reversible, insoluble condensates at night in an ATP-dependent manner [ 432 ]; therefore, it is not unreasonable to hypothesize that the relationship between melatonin, MLOs, ATP, and RNA was already in existence at ~3.5 Ga.…”

Exogenous melatonin on Physiological and Yield Traits of Cassava (Manihot esculenta Crantz) under Salt Stress

“…Similarly, the maize seedlings showed higher transpiration rate and photosynthetic rate under drought (Qiao et al, 2020;Huang et al, 2019). Hwang et al (2020) proved that the antioxidants present in melatonin enhanced photosynthesis. Thus exogenous melatonin exhibits a major role in ROS reduction and increases antioxidants and secondary metabolites (Shakhawat et al, 2020;Shakeel et al, 2020).…”