Maize Genomics and Genetics 2024, Vol.15, No.4, 160-170 http://cropscipublisher.com/index.php/mgg 161 The primary goal of this study is to provide a comprehensive overview of the current research status of maize chloroplast genomes, emphasizing their importance in understanding the domestication process. The study will summarize the methods used for sequencing and analyzing maize chloroplast genomes, analyze key findings from recent studies on the structure, function, and evolution of maize chloroplast genomes, and discuss how these findings contribute to a broader understanding of maize domestication. Additionally, the study will discuss the impact of chloroplast genome variation on maize physiology, development, and stress responses, identify gaps in current knowledge, and propose directions for future research. By achieving these objectives, this study will contribute to a deeper understanding of the role of chloroplast genomes in maize biology and their potential applications in crop improvement. 2 The Chloroplast Genome of Zea 2.1 Structure and organization The chloroplast genome of Zea, like many other plant species, exhibits a typical quadripartite structure. This structure includes a large single copy (LSC) region, a small single copy (SSC) region, and a pair of inverted repeat (IRa and IRb) regions. Such organization is consistent with the chloroplast genomes of other species within the Poaceae family and beyond (Li et al., 2019a; 2020a; Yang et al., 2022). The LSC and SSC regions are separated by the IR regions, which are generally more conserved compared to the single copy regions (Biju et al., 2019). This structural organization is crucial for maintaining the stability and functionality of the chloroplast genome. In maize, the chloroplast genome encodes approximately 110~130 genes, including those essential for photosynthesis (e.g., rbcL, psaA, psbA) and genes involved in transcription and translation (e.g., rpoB, rpoC1). The organization of these genes is highly conserved among angiosperms, with variations in non-coding regions contributing to interspecies diversity. 2.2 Function and significance The chloroplast genome plays a vital role in photosynthesis and other essential metabolic processes. It encodes genes involved in the photosynthetic machinery, including those for the photosystem I and II complexes, ATP synthase, and the cytochrome b6f complex (Li et al., 2020a; 2020b). These genes are vital for the conversion of light energy into chemical energy, enabling the plant to produce the carbohydrates necessary for growth and development. Additionally, the chloroplast genome contains genes for ribosomal RNAs (rRNAs), transfer RNAs (tRNAs), and various proteins necessary for chloroplast function and maintenance. The presence of these genes underscores the significance of the chloroplast genome in sustaining the energy requirements of the plant through photosynthesis (Li et al., 2019b; Orton et al., 2020). 2.3 Comparison with other plant species When comparing the chloroplast genome of Zea with those of other plant species, several similarities and differences can be observed. The overall structure, including the presence of LSC, SSC, and IR regions, is highly conserved across different species, such as those in the Zingiberaceae family (Li et al., 2019a; 2020b; Yang et al., 2022). Studies have found that the chloroplast genes of maize, rice, and wheat evolve at similar rates among grass species, with photosynthesis genes undergoing strong purifying selection (Matsuoka et al., 2002). However, variations in the size of these regions and the presence or absence of certain genes can occur. For instance, the absence of the rps19 gene in some Zingiberaceae species due to the expansion of the LSC region highlights the dynamic nature of chloroplast genome evolution (Yang et al., 2022). Additionally, the identification of highly divergent regions and single nucleotide polymorphisms (SNPs) in various species provides valuable markers for phylogenetic studies and species identification (Li et al., 2020a; 2020b; Yang et al., 2022). The chloroplast genome of Zea is structurally and functionally similar to those of other plant species, with specific variations that contribute to its unique evolutionary path. These insights into the chloroplast genome of Zea enhance understanding of maize domestication and its adaptation to different environments.
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