Transcriptome and metabolome profiling of unheading in F1 hybrid rice

Heading date is a crucial agronomic trait. However, rice usually delays heading due to the photoperiod, temperature, hormones or age. The present research was conducted to analyze the mechanism controlling heading date in F-1 hybrid rice. We constructed two test-crossing populations using two introgression lines (ILs), P20 and P21 coming from SH527/FH838 as the male parent, respectively, and male sterile line Jin23A as the female parent. Meanwhile, the F, hybrids of H20, obtained by mating P20 with Jin23A and having no heading, and H21, from the crossing between P21 and Jin23A having normal heading, were both observed under long days. Here, we analyzed the photoperiodic response of F, hybrids by transcriptome and metabolome profiling. The greater differences displayed in the transcriptome and the metabolome were caused by photoperiod (exogenous) instead of genes (endogenous). The coping mechanism resulted from long days (LD) in H20, leading to differences in the circadian rhythm and glutathione metabolism relative to other samples. The circadian oscillator and GSH/GSSG cycle typically regulate ROS homeostasis, and both of them are responsible for modulating ROS in H20 under LD condition. Both circadian rhythm genes and the reported genes related to heading date function via the DHD1/OsMFT1-Ehd1-RFT1-OsMADS14/OsMADS18 pathway and the glutathione metabolism pathway by regulating oxidative reduction processes. Both pathways are involved in the heading process and they interacted through the oxidative reduction process which was induced by photoperiod regulation, and all of them collectively modulated the heading process. The results of this study will be helpful for unraveling the mechanism of F-1 hybrid responses to unheading under LD condition.