Metabolomic and transcriptomic basis of photoperiodic response regulation in broomcorn millet (Panicum miliaceum L.).

To elucidate the mechanisms underlying photoperiodic responses, we investigated the genomic and metabolomic responses of two broomcorn millet (Panicum miliaceum L.) genotypes. For this purpose, light-insensitive (D32) and light-sensitive (M51) genotypes were exposed to a 16 h photoperiod (long-day (LD) conditions) and an 8 h photoperiod (short-day (SD) conditions), and various transcriptomic and metabolomic changes were investigated. A total of 1664, 2564, 13,017, and 15548 DEGs were identified in the SD-D, LD-D, LD-M, and SD-M groups, respectively. Furthermore, 112 common DEGs were identified as well. Interestingly, most DEGs in the different groups were associated with photosynthesis and phenylpropanoid and carotenoid biosynthesis. In addition, 822 metabolites were identified under different treatments. The main metabolites, including L-malic and fumaric acids, were identified in the negative mode, whereas brucine and loperamide were identified in the positive mode. KEGG analysis revealed that the metabolites in the different groups were enriched in the same metabolic pathway of the TCA cycle. Furthermore, in negative mode, the metabolites of M51 were mainly D-glucose, whereas those of D32 were mainly L-malic and fumaric acids. One photoperiod candidate gene (C2845_PM11G01290), annotated as ATP6B, significantly increased the levels of L-malic and fumaric acids. In conclusion, our study provides a theoretical basis for understanding the molecular mechanisms of photoperiodic response regulation and can be used as a reference for marker development and resource identification in Panicum miliaceum L..