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

Ok Jin Hwang,Kyoungwhan Back

doi:10.3390/molecules26041075

Abstract

We investigated the relationship between the blue-light photoreceptor cryptochrome (CRY) and melatonin biosynthesis by generating RNA interference (RNAi) transgenic rice plants that suppress the cryptochrome 1b gene (CRY1b). The resulting CRY1b RNAi rice lines expressed less CRY1b mRNA, but not CRY1a or CRY2 mRNA, suggesting that the suppression is specific to CRY1b. The growth of CRY1b RNAi rice seedlings was enhanced under blue light compared to wild-type growth, providing phenotypic evidence for impaired CRY function. When these CRY1b RNAi rice plants were challenged with cadmium to induce melatonin, wild-type plants produced 100 ng/g fresh weight (FW) melatonin, whereas CRY1b RNAi lines produced 60 ng/g FW melatonin on average, indicating that melatonin biosynthesis requires the CRY photoreceptor. Due to possible feedback regulation, the expression of melatonin biosynthesis genes such as T5H, SNAT1, SNAT2, and COMT was elevated in the CRY1b RNAi lines compared to the wild-type plants. In addition, laminar angles decreased in the CRY1b RNAi lines via the suppression of brassinosteroid (BR) biosynthesis genes such as DWARF. The main cause of the BR decrease in the CRY1b RNAi lines seems to be the suppression of CRY rather than decreased melatonin because the melatonin decrease suppressed DWARF4 rather than DWARF.

Highlights

Light-dependent melatonin synthesis occurs in some plant species, whereas in other plants, melatonin exhibits a nocturnal increase similar to that in animals [1,2,3,4]
cryptochrome 1b gene (CRY1b) was significantly suppressed in the three CRY1b RNA interference (RNAi) lines, whereas CRY1a and CRY2 mRNA levels were comparable to those in the wild type according to Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) and semiquantitative RT-PCR analyses
Seedling length was longer in the CRY1b RNAi lines than in the wild type when seedlings were grown under blue light, as was the length of the second leaf sheath (Figure 2d–f)

Summary

Introduction

Light-dependent melatonin synthesis occurs in some plant species, whereas in other plants, melatonin exhibits a nocturnal increase similar to that in animals [1,2,3,4]. The major known functions of melatonin are plant defense responses against both biotic and abiotic stresses [12,13], plant growth, and reproduction [7,14]. Melatonin is closely involved in conferring tolerance against endoplasmic reticulum stress [15,16], salt [17,18], pathogens [19,20], high temperatures [21,22], high light stress [23], and other stresses [24]. Melatonin plays roles in plant growth and reproduction, including the synthesis of secondary metabolites [25,26], germination [27], seed longevity [28], hormone synthesis [29,30], fruit yield [31], and other processes [32]

Methods

Results

Conclusion