Plant Gene and Traits 2024, Vol.15, No.3, 129-140 http://genbreedpublisher.com/index.php/pgt 131 stabilizing it and preventing its degradation. The phosphorylated ABI5 then activates ABA-responsive genes, leading to the suppression of germination. This feedback loop highlights the critical role of ABA in regulating seed germination. PYLs maintain the stability of ABI5, which in turn regulates the expression of ABA-responsive genes and PYLs, ensuring a tightly controlled germination process in response to environmental cues. This mechanism ensures seeds only germinate under favorable conditions. Figure 1 A working model for the cooperation of PYLs and ABI5 in seed germination (Adopted from Zhao et al., 2020) Image caption: The abscisic acid (ABA) receptor PYLs maintain the stability of ABI5 to activate the expression of ABA-responsive genes and ABI5 plays a role in the feedback regulation of ABA signaling by maintaining the expression of PYLs (Adopted from Zhao et al., 2020) 3.2 Role of environmental factors in gene regulation Environmental factors such as light and temperature significantly influence gene expression during seed germination. Light, for example, is a critical environmental cue that affects the degradation of repressors like PHYTOCHROME INTERACTING FACTOR 1 (PIF1), thereby promoting germination through hormonal changes (Jiang et al., 2021). High temperatures can delay germination by reactivating the expression of transcription factors like FUSCA3 (FUS3), which in turn modulates ABA levels to inhibit germination under suboptimal conditions (Chiu et al., 2012). Furthermore, the histone H3K27 demethylase REF6 has been identified as a positive regulator of light-initiated seed germination, indicating that epigenetic modifications also play a role in how environmental signals are integrated into the germination process (Wang et al., 2023). 3.3 Interaction between genetic and epigenetic factors The transition from seed to seedling involves complex interactions between genetic and epigenetic factors. Key transcription factors such as LEAFY COTYLEDON1 and 2 (LEC1 and LEC2), ABSCISIC ACID INSENSITIVE3 (ABI3), and FUS3 are crucial for maintaining seed dormancy and need to be suppressed for germination to proceed. This suppression is mediated by chromatin remodeling complexes like POLYCOMB REPRESSIVE COMPLEX 1 and 2 (PRC1 and PRC2) (Smolikova et al., 2021). Additionally, histone modifications, such as the demethylation of H3K27 by REF6, play a significant role in activating gene expression necessary for germination (Wang et al., 2023). These epigenetic changes ensure that the genetic programs required for seed maturation are turned off, while those needed for seedling development are activated, thereby facilitating a smooth transition from dormancy to active growth. In summary, the regulation of gene expression during pine seed germination is a multifaceted process involving hormonal signals, environmental cues, and intricate genetic and epigenetic interactions (Miransari and Smith, 2014). Understanding these mechanisms provides valuable insights into the fundamental processes governing plant development and adaptation.
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