Plant Gene and Trait 2025, Vol.16, No.3, 92-103 http://genbreedpublisher.com/index.php/pgt 93 What this study wants to do is actually to connect the current research clues on the regulation of sugarcane photosynthesis, focusing on the key factors that affect the C4 pathway and carbon metabolism. For example, what are the genes that control the relevant metabolic enzymes? How are they regulated by upstream networks or transcription factors? What changes will the combination of genetics and environment bring to yield? We are particularly interested in new discoveries in transcriptomics and gene editing in recent years, such as the role of certain miRNAs and TFs in regulating the expression of C4-related genes. We hope that by summarizing these molecular genetics, physiological mechanisms and breeding strategies, we can provide some new ideas for improving the photosynthetic efficiency and yield of sugarcane and other C4 crops in the future - after all, the climate is changing, and the sustainable development of agriculture must keep pace. 2 Overview of Photosynthesis in Sugarcane 2.1 Structure and function of C4 photosynthesis in sugarcane Not all plants survive by using a single photosynthesis mechanism. Crops like sugarcane use the C4 pathway, and the structure in its leaves is different, scientifically called the “Kranz structure”. To put it simply, the mesophyll cells (M) and bundle sheath cells (BS) are arranged in a circle like a “nesting doll”. The carbon dioxide in the air is first captured by the PEPC enzyme in the mesophyll cells to produce a four-carbon compound. Then this four-carbon cargo is sent all the way to the bundle sheath cells, where carbon dioxide is released, and Rubisco comes on the scene to pull it into the Calvin cycle (Figure 1). In the final analysis, this "division of labor and cooperation" method helps sugarcane to complete photosynthesis steadily in hot, dry, and light-intensive environments, and the interference of photorespiration is much less (De Oliveira Dal’Molin et al., 2010). 2.2 Comparison of C3 andC4 mechanisms in relation to carbon assimilation C3 plants and C4 plants follow two different photosynthesis routes, and the structural differences make them behave very differently in different environments. Take C3 plants, for example, they arrange the fixation of CO₂ and the subsequent Calvin cycle in the mesophyll cells. The problem is that this arrangement makes it easy for Rubisco to “recognize the wrong object” and accidentally pull in oxygen, resulting in increased photorespiration - especially when the temperature is high and CO₂ is insufficient. C4 plants like sugarcane cleverly separate these two steps: first use PEPC enzymes to capture CO₂ in the mesophyll cells, and then hand it over to the bundle sheath cells to continue the Calvin cycle. In this way, not only is photorespiration minimized, but the use of water and nitrogen is also more efficient. This also explains why C4 plants are more “durable” than C3 plants in hot, drought, and strong light environments (Yadav and Mishra, 2020; Yadav et al., 2020; Cui, 2021). 2.3 Significance of Kranz anatomy and CO2 concentrating mechanisms When it comes to C4 plants, the concept of the “Kranz structure” cannot be avoided. It is not a rare design. High-yield crops such as sugarcane and corn are equipped with this structure. The mesophyll cells and bundle sheath cells are arranged very compactly. In this structure, carbon dioxide is like being centrally supplied and can be efficiently used in the bundle sheath cells, thus preventing Rubisco from being “misled” by oxygen. Interestingly, although most C4 plants rely on this “cell cooperation” method, there are always exceptions in nature - some species can even complete similar concentration processes with only a single cell. Regardless of the method, the idea behind it is actually the same: how to use carbon dioxide more valuable. With more research on this type of mechanism, perhaps in the future we can “graft” the advantages of C4 onto C3 crops. After all, who wouldn’t want to make them more water-saving and efficient? 3 Molecular Regulation of the C4 Photosynthetic Pathway 3.1 Key genes encoding enzymes of the C4 cycle In the final analysis, sugarcane’s C4 photosynthesis relies on a complex and coordinated enzyme system. Several key enzymes, such as PEPC, NADP-ME and PPDK, play a core role in the whole process. They are not simply “commanded by a unified command”, but are distributed in different cells (mesophyll and bundle sheath), each performing its own duties. For example, the Pdk gene is responsible for encoding two PPDK proteins, one in the chloroplast and the other in the cytoplasm, and different regulatory sequences make them “return to their respective positions”. There is also Me1, which produces NADP-ME specifically for C4 metabolism, and also
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