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

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 gene (). The resulting RNAi rice lines expressed less mRNA, but not or mRNA, suggesting that the suppression is specific to . The growth of RNAi rice seedlings was enhanced under blue light compared to wild-type growth, providing phenotypic evidence for impaired CRY function. When these RNAi rice plants were challenged with cadmium to induce melatonin, wild-type plants produced 100 ng/g fresh weight (FW) melatonin, whereas 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 , , , and was elevated in the RNAi lines compared to the wild-type plants. In addition, laminar angles decreased in the RNAi lines via the suppression of brassinosteroid (BR) biosynthesis genes such as . The main cause of the BR decrease in the RNAi lines seems to be the suppression of CRY rather than decreased melatonin because the melatonin decrease suppressed rather than .