Rice Genomics and Genetics 2025, Vol.16, No.4, 211-218 http://cropscipublisher.com/index.php/rgg 212 2 Overview of Molecular Mechanisms Regulating Rice Flowering Time 2.1 Photoperiod pathway and its key genes The photoperiodic pathway is the main way to regulate the flowering time of rice, enabling it to flower in the appropriate season. Rice is a facultative short-day plant. Under short-day (SD) conditions, it flowers earlier, while under long-day (LD) conditions, it flowers later. There are several important genes in this pathway, such as the heading stage 1 gene (Hd1) and the early heading stage 1 gene (Ehd1). Hd1 is a homologous gene of the CONSTANS gene in Arabidopsis thaliana and has dual functions: under short-day conditions, it can activate the heading period 3a gene (Hd3a) to promote flowering; Under long-day conditions, it inhibits flowering, and this effect is achieved through interaction with the heading 8 gene (DTH8). The DTH8-Hd1 complex increases the H3K27me3 modification on the Hd3a gene, thereby reducing its expression and delaying flowering under long-day conditions (Figure 1) (Lee and An, 2015; Du et al., 2017; Sohail, 2023; Yin et al., 2023). Ehd1 is a positive regulatory gene specific to rice. It can induce the expression of Hd3a and rice flowering locus T1 (RFT1), and promote flowering independently of Hd1, especially under long-day conditions (Hori et al., 2016; Nunez and Yamada, 2017). Other regulatory factors, such as Ghd7 and OsCOL16, can further regulate the photopedic network by inhibiting Ehd1 andHd3a to ensure precise control of flowering (Wu et al., 2017; Sun et al., 2022). Figure 1 93-11 Contains anHd1allele with a mutation in the CCT domain-encoding region (Adopted from Du et al., 2017) 2.2 Vernalization pathway and temperature signal sensing mechanisms Vernalization (long-term low-temperature induction of flowering) is common in temperate grains and Arabidopsis thaliana, but rice, which grows in tropical and subtropical regions, is not sensitive to vernalization. However, temperature still affects the flowering time of rice. Temperature signals act in conjunction with photoperiodic pathways to regulate the expression of key genes such as Ehd1 and Hd3a. Temperature changes can alter the activity of these genes, thereby affecting flowering time and environmental adaptability (Shrestha et al., 2014; Shim and Jang, 2020; Wei et al., 2020). The combination of temperature and photoperiodic signals enables rice to flexibly adjust its flowering according to the season and climate. 2.3 Interaction between hormone signaling pathways and flowering regulation Hormone signals such as jasmonic acid (JA), gibberellin (GA), and abscisic acid (ABA) also interact with the flowering regulatory network, affecting the flowering time. For instance, the OsMYC2-JA feedback loop can regulate the remodeling of the flower tissue cell wall, thereby affecting the circadian flowering rhythm, which is important for propagation and hybrid seed production (Zhu et al., 2024). Hormones can affect the expression or
RkJQdWJsaXNoZXIy MjQ4ODYzNA==