Bioscience Methods 2024, Vol.15, No.4, 149-161 http://bioscipublisher.com/index.php/bm 150 2 Photosynthetic Machinery in Maize 2.1 Structure and function of photosynthetic components The photosynthetic machinery in maize, like in other plants, is located within the thylakoid membranes of chloroplasts. This machinery is responsible for converting light energy into chemical energy through a series of complex processes. The primary components include Photosystems I and II (PSI and PSII), light-harvesting complexes (LHCs), the electron transport chain, and ATP synthase. These components work together to capture light energy, transfer electrons, and synthesize ATP and NADPH, which are essential for the Calvin cycle and other metabolic processes. 2.2 Photosystems I and II: composition and roles Photosystem I (PSI) and Photosystem II (PSII) are integral to the photosynthetic process. PSI is composed of multiple subunits, including a core complex and light-harvesting complexes (LHCI). In maize, PSI can form super complexes with LHCI and LHCII, which help in balancing energy flow under fluctuating light conditions (Pan et al., 2018). PSII, on the other hand, is primarily responsible for the initial capture of light energy and the splitting of water molecules to release oxygen. Both photosystems work in tandem to drive the linear electron flow, which is crucial for the production of ATP and NADPH (Pan et al., 2018; Crepin et al., 2019). 2.3 Light Harvesting Complexes (LHC) and their function Light-harvesting complexes (LHCs) are essential for capturing light energy and transferring it to the reaction centers of PSI and PSII. In maize, LHCs are composed of chlorophylls and carotenoids bound to specific proteins. These complexes not only increase the absorption cross-section of the photosystems but also play a critical role in photoprotection by dissipating excess light energy (Lokstein et al., 2021; Wang et al., 2021). The trimeric LHCII is the main antenna complex of PSII, and its phosphorylation state can influence its association with PSI, thereby optimizing energy distribution between the photosystems (Pan et al., 2018; Vayghan et al., 2021). 2.4 Electron transport chain and atp synthesis The electron transport chain (ETC) in maize involves a series of protein complexes and mobile electron carriers that facilitate the transfer of electrons from PSII to PSI. This process generates a proton gradient across the thylakoid membrane, which drives ATP synthesis through ATP synthase. The ETC includes components such as cytochrome b6f complex, plastoquinone, and plastocyanin. Additionally, cyclic electron flow around PSI can occur, which helps in generating additional ATP without the production of NADPH, thus balancing the ATP/NADPH ratio required for the Calvin cycle (Steinbeck et al., 2018). 2.5 Carbon fixation pathways (C3, C4, CAM) and their relevance to maize Maize utilizes the C4 carbon fixation pathway, which is highly efficient in hot and dry environments. This pathway involves the initial fixation of CO2 into a four-carbon compound, oxaloacetate, which is then converted into malate. Malate is transported to bundle-sheath cells, where it releases CO2 for the Calvin cycle. This mechanism minimizes photorespiration and enhances water-use efficiency, making maize well-suited for growth in arid conditions. The C4 pathway is a significant evolutionary adaptation that allows maize to maintain high photosynthetic efficiency under stress conditions (Jang and Mennucci, 2018). By understanding the intricate details of the photosynthetic machinery in maize, researchers can explore ways to enhance crop productivity and stress tolerance, which are crucial for meeting the growing global food demand. 3 Molecular Regulation of Photosynthesis in Maize 3.1 Gene expression profiles underlying photosynthesis The gene expression profiles underlying photosynthesis in maize are complex and involve the coordinated expression of numerous genes. Single-cell RNA sequencing (scRNA-seq) has revealed that various transcription factor (TF) families, such as WRKY, ERF, NAC, MYB, and Heat stress transcription factors (HSF), play significant roles in the early stages of mesophyll cell development, which is crucial for photosynthesis (Figure 1) (Tao et al., 2022). Additionally, the compartmentation of photosynthesis gene expression in maize is influenced
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