Legume Genomics and Genetics 2025, Vol.16, No.5, 234-244 http://cropscipublisher.com/index.php/lgg 235 This study will systematically analyze the molecular pathways of the cold resistance response of adzuki beans, review the physiological and biochemical effects of cold stress, and then explore the latest research results on the unique gene regulation, signal network and defense mechanism of adzuki beans, identify key molecular regulatory factors, clarify their roles in cold resistance adaptation, and propose strategies for breeding or biotechnology improvement. By deepening the understanding of the cold resistance response pathway, this study has scientific significance for breeding cold-resistant adzuki bean varieties and is conducive to conducting more extensive research on crop stress biology. 2 Cold Perception and Initial Signal Transduction Mechanisms in Adzuki Bean 2.1 Perception of low temperature through membrane fluidity changes and cold sensors When the temperature drops sharply, plant cells do not immediately activate their response through a certain "cold sensor". More commonly, the plasma membranes of adzuki beans and other plants first become less flexible - this step of change can quickly be captured by the protein or lipid signal chains on the membrane. In Arabidopsis thaliana, studies have found that low temperatures activate diacylglycerol kinase (DGK), which then converts diacylglycerol into phosphatidic acid. Such molecules act as "middlemen" in signal transduction (Wei et al., 2021). Although it is not yet fully clarified which "receptors" in adzuki beans are dominant in the response, from a conservative perspective, the mechanism is likely to be similar. 2.2 Activation and regulation of calcium signaling (Ca2+) under cold stimuli Hardly any cold stress response skips the calcium signal step. In plants such as adzuki beans, when the temperature drops, calcium ions will rapidly flood into the cytoplasm, which is one of the earliest signals of the cold response. This signal does not remain on the surface but is "read" by calcium-binding proteins such as calmodulin or CDPK and continues to be transmitted downward (Figure 1) (Ding et al., 2022; Yin et al., 2023). Research on model plants and other leguminous plants also points to a consensus: Ca²⁺ not only regulates the expression of cold-related genes but may also act as a "switch" for other adaptive mechanisms. Adzuki beans themselves also carry GLR genes, which means they are not "outsiders" in terms of calcium flux sensing. 2.3 Roles of reactive oxygen species (ROS) and nitric oxide (NO) in early signaling events When the weather gets cold, calcium ions alone are not enough to make it lively. Many plants, Arabidopsis thaliana is a typical example, will simultaneously experience a wave of ROS and NO. Although they sound like "harmful elements", in fact, these two are the important "megaphones" in the early signals. With the help of NADPH oxidase, ROS production activates cold-related transcription factors and further strengthens Ca²⁺ signaling (Wei et al., 2021). Meanwhile, the emergence of NO is no accident. Together with ROS, it regulates gene expression, protein activity, and even the REDOX state of cells. It was the collaborative efforts of these initial small molecules that truly initiated the "first act" of the cold response of adzuki beans. 3 Transcriptional Regulation and Core Cold-Responsive Pathways 3.1 Activation and regulatory mechanisms of CBF/DREB transcription factors When cold stimulation is first sensed, transcription factors such as CBF/DREB are quickly activated. They are among the first batch of regulatory elements to appear in the plant's cold response. Their goal is clear - to lock onto the DRE/CRT sequence in the promoter of the COR gene and initiate downstream expression (Abdullah et al., 2022). These activated COR genes guide the synthesis of some antifreeze proteins and osmotic regulatory substances, which help maintain cell stability and antifreeze performance. However, this pathway does not operate in isolation. Most of it belongs to the ABA-independent pathway, and its regulatory mechanism does not rely on abscisic acid. However, the expression level of CBF itself is not always constant and can also be affected by post-transcriptional and even post-translational modifications. That is to say, plants do not simply make the CBF work, but rhythmically "regulate the regulatory factors" to cope with different degrees of low-temperature stress (Wang et al., 2024a).
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