Melatonin regulates lily bulblet development through the LoBPM3-LoRAV module

Melatonin regulates lily bulblet development; however, the key interactions have not yet been determined. In this study, we found that adding 20 μM melatonin to the growth medium increased the bulblet circumference and the trehalose and starch content. Moreover, the expression of numerous genes involved in cell proliferation and carbohydrate accumulation were upregulated. Further analysis showed that melatonin downregulated the expression of LoRAV and upregulated the expression of LoBPM3 at an early stage. Cloning and bioinformatics analysis showed that LoRAV is 1056 bp in length and encodes a protein with two structural domains, namely, AP2 and B3; the encoded protein is localized to the nucleus and has no self-activation activity, and this protein interacts with LoBPM3. The expression of LoTCP4 and LoAMY was upregulated, while the expression of LoAGPase, LoCYCB2-1, and LoPCNA was inhibited when LoRAV was transiently overexpressed. However, the trends in the expression of the genes mentioned above, except LoAGPase and LoAMY, were reversed when LoRAV-OE was treated with melatonin. Interestingly, the expression of LoRAV, LoTCP4 and LoAMY was inhibited, and the expression of LoCYCB2-1 was upregulated by transient overexpression of LoBPM3, but the expression of LoBPM3 was not regulated by LoRAV overexpression. Based on these data, we suggest that melatonin promoted bulb development, which was partly associated with regulation of the LoBPM3-LoRAV module; thus, LoRAV negatively regulates cell proliferation of bulblets, and LoBPM3 is located upstream of LoRAV and attenuates its expression.