Melatonin induction and its role in high light stress tolerance in Arabidopsis thaliana

Abstract

In plants, melatonin is a potent bioactive molecule involved in the response against various biotic and abiotic stresses. However, little is known of its defensive role against high light (HL) stress. In this study, we found that melatonin was transiently induced in response to HL stress in Arabidopsis thaliana with a simultaneous increase in the expression of melatonin biosynthetic genes, including serotonin N-acetyltransferase1 (SNAT1). Transient induction of melatonin was also observed in the flu mutant, a singlet oxygen ( O )-producing mutant, upon light exposure, suggestive of melatonin induction by chloroplastidic O against HL stress. An Arabidopsis snat1 mutant was devoid of melatonin induction upon HL stress, resulting in high susceptibility to HL stress. Exogenous melatonin treatment mitigated damage caused by HL stress in the snat1 mutant by reducing O production and increasing the expression of various ROS-responsive genes. In analogy, an Arabidopsis SNAT1-overexpressing line showed increased tolerance of HL stress concomitant with a reduction in malondialdehyde and ion leakage. A complementation line expressing an Arabidopsis SNAT1 genomic fragment in the snat1 mutant completely restored HL stress susceptibility in the snat1 mutant to levels comparable to that of wild-type Col-0 plants. The results of the analysis of several Arabidopsis genetic lines reveal for the first time at the genetic level that melatonin is involved in conferring HL stress tolerance in plants.

Melatonin‐deficient rice plants show a common semidwarf phenotype either dependent or independent of brassinosteroid biosynthesis

“…17,24 Owing to the successful cloning of the melatonin biosynthetic genes mentioned above, many transgenic rice plants that either overexpress or suppress these genes have been generated: melatonin-rich plants exhibit increased yield in conjunction with resistance against senescence and cadmium, 36 whereas melatonin-deficient plants have a reduced yield with increased susceptibility to salt, cold, pathogens, and high light. 13,23,[37][38][39] We found a previously unrecognized phenotype that occurred in the melatonin-deficient snat2 rice with a downregulated SNAT2 gene. The snat2 rice has a semidwarf erect-leaf phenotype, reminiscent of a BR-deficient phenotype.…”

“…SNAT is the penultimate enzyme step responsible for the synthesis of N ‐acetylserotonin, which is further catalyzed into melatonin by various O ‐methyltransferases, including COMT . Owing to the successful cloning of the melatonin biosynthetic genes mentioned above, many transgenic rice plants that either overexpress or suppress these genes have been generated: melatonin‐rich plants exhibit increased yield in conjunction with resistance against senescence and cadmium, whereas melatonin‐deficient plants have a reduced yield with increased susceptibility to salt, cold, pathogens, and high light …”

“…Melatonin is essential for normal growth and development, such as stomatal closure, the auxin signaling pathway, starch synthesis, plant regeneration, and root formation, as well as for defense against an array of biotic and abiotic stressors, including high light, pathogens, salt, senescence, and high temperature, among others . The functional roles of melatonin in plants are associated with crosstalk with plant hormones, such as auxin, cytokinin, salicylic acid, and abscisic acid …”

“…stressors, including high light, 13 pathogens, 14 salt, 15 senescence, 16,17 and high temperature, 18 among others. 19 The functional roles of melatonin in plants are associated with crosstalk with plant hormones, such as auxin, cytokinin, salicylic acid, and abscisic acid.…”

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

“…In response to abiotic stresses, such as drought and high light conditions, chloroplasts produce more ROS, such that more ROS scavengers are required, including antioxidants and antioxidant enzymes [44]. The close relationship between high photosynthesis activity and peak melatonin synthesis under the R + B condition has a genetic basis; the Arabidopsis melatonin-deficient snat1 knockout mutant showed enhanced susceptibility to high light stress [45]. In addition, chloroplasts are major sites for melatonin biosynthesis, and contain the penultimate SNAT enzyme and key regulatory enzymes, such as M2H and N-acetylserotonin deacetylase [46][47][48].…”