RGG_2025v16n1

Rice Genomics and Genetics 2025, Vol.16, No.1, 50-60 http://cropscipublisher.com/index.php/rgg 52 red light and far-red light, which directly affects the growth rhythm of rice. For example, phytochrome B (phyB), this guy is best at sensing the ratio of red light to far-red light (R\:FR ratio). However, it should be noted that not every time the R\:FR ratio decreases, the stem must be elongated - some varieties are slow to respond to shade, but in most cases, they will accelerate stem elongation by producing more auxin and gibberellin (Pierik and Ballaré, 2020; Ma, 2024). In addition, this guy can also intervene in the defense system and adjust the jasmonic acid signaling pathway so that plants can have more tricks when facing pathogens. When it comes to photoperiod control of flowering, phytochrome A (phyA) and B are not always on the same side: sometimes they go their own way, and sometimes they come together to cooperate, depending on how the light conditions are. Sometimes you may think that the "blue light switches" in the leaves are really not simple - cryptochromes and phytochromes are actually blue light receptors, the purpose of which is to make photosynthesis more efficient and various light reactions more flexible. Let's talk about cryptochromes (cry1 and cry2): they help seedlings gain a foothold, calibrate circadian rhythms, and can also drive plants from the "eating nutrients" stage to the "flowering and fruiting" stage. However, there are a few strains that are not so dependent on them. All of this is achieved by them working in concert with other photoreceptors and signal molecules. As for phytochromes, don't think that it only controls red light-it can also sense blue light, control phototropism, light-induced stomatal opening and chloroplast swinging, which is the key to truly turning light energy into nutrients. After phytochromes receive photons, they will change their "body" and activate their own protein kinases, and then a series of signals will unfold. 3.2 Signal transduction pathways regulating light responses Sometimes you might think that the signaling pathways in rice are like a complex social network - light receptors and transcription factors are pieced together and influence each other. But don't forget that not all links are perfect, and some transcription factors respond differently in different varieties. Let's talk about the most conspicuous ones first: phytochromes, cryptochromes, and phytochromes, once they receive light signals, they will set off a series of cascade reactions, reorganize the transcription program, and mark some signaling proteins for degradation. By the way, the COP1/SPA ubiquitin E3 ligase complex and PIF transcription factors are key hubs, and their activity is directly dragged around by light receptors (Pierik and Ballaré, 2020). Another detail - under light, phytochromes and UVR8 have to move to the nucleus to gather, and cryptochrome cry2 also has to accumulate in the nucleus. This step is crucial for activating light-responsive genes (Figure 1) (Jing and Lin, 2020). However, the most interesting thing is that this system is ultimately designed to allow rice plants to flexibly adjust their growth and development according to the surrounding light. 3.3 Influence of photoperiod on rice flowering and yield The flowering time and yield of rice are actually closely related to the length of day and night (i.e., photoperiod). However, it is not that simple. Rice is a plant that flowers only when the daylight is short (short-day plant). Speaking of this, we have to mention phytochromes, especially phyA and phyB, which are in sync with the biological clock and can control flowering genes, and are particularly important in sensing photoperiods. Interestingly, the Hd1 gene (a relative of the Arabidopsis CO gene in rice) follows the rhythm of the biological clock to regulate the expression of FT homologous genes, which is the key to determining when to flower (Su et al., 2016). Moreover, there is a blue light response protein called OsHAL3, which can work with Hd1 to adjust the flowering time under different light conditions. You see, the entire network of rice's light sensing and signal transmission is indeed quite complex. 4 Integration of Temperature and Light Signaling in Rice 4.1 Cross-talk between temperature and light signaling pathways Sometimes you feel that temperature and light signals in rice plants are like two old friends who are reluctant to sit together - they always have to find various excuses to chat. First of all, phytochrome B (phyB) is not only concerned with light, but also takes care of temperature. Once it is busy, it will pass information to the regulatory bosses below, such as phytochrome interacting factor 4 (PIF4) and constitutive photomorphogenic protein 1

RkJQdWJsaXNoZXIy MjQ4ODYzNA==