Maize Genomics and Genetics 2024, Vol.15, No.1, 36-48 http://cropscipublisher.com/index.php/mgg 37 2 Origin and Domestication 2.1 Historical context of teosinte and maize domestication The domestication of maize from its wild ancestor, teosinte, represents one of the most significant agricultural transformations in human history. This process began approximately 9 000 years ago in the Balsas River Valley of southern Mexico. Archaeological evidence from Guilá Naquitz, Oaxaca, indicates that agricultural selection of domesticated teosinte was underway by around 4 200 B.C. (Benz, 2001). The transition from foraging to farming marked a pivotal change in human societies, allowing for settled communities and the development of complex civilizations. Maize (Zeamays ssp. mays) and its closest wild relatives, the teosintes (Zeamays ssp. parviglumis and Zeamays ssp. mexicana), exhibit stark differences in morphology despite their genetic similarities. This domestication process involved significant modifications to teosinte's physical characteristics, making it more suitable for human consumption and cultivation (Panda et al., 2020). 2.2 Genetic evidence for domestication events Genetic studies have played a crucial role in unraveling the complex history of maize domestication. Phylogenetic analyses based on multilocus microsatellite genotyping indicate that all modern maize varieties descended from a single domestication event in southern Mexico about 9 000 years ago (Matsuoka et al., 2002). This finding challenges earlier hypotheses that proposed multiple independent domestication events. The genetic diversity observed in maize today can be attributed to gene flow from various teosinte taxa into the maize gene pool, both during and after domestication. Gene flow from teosinte has contributed to the genetic variability seen in maize, allowing for adaptation to diverse environments and resilience to biotic and abiotic stresses (Warburton et al., 2011). Comparative genomics studies have identified significant genetic variations, such as copy number variations (CNVs) and presence-absence variations (PAVs), between maize and teosinte. These genetic differences have been crucial in understanding the domestication process and identifying genes under strong selection during this period (Swanson-Wagner et al., 2010). 2.3 Morphological changes during domestication The domestication of maize involved dramatic morphological changes from its wild ancestor, teosinte. These changes were primarily driven by human selection for traits that enhanced the utility and productivity of the plant. One of the most significant morphological changes was the modification of the ear structure. In teosinte, the ear is composed of a few small, hard kernels enclosed in a hard casing, making it difficult for human consumption. In contrast, domesticated maize has large, exposed kernels that are easily accessible (Wang et al., 2005). The teosinte branched1 (tb1) gene played a critical role in this transformation. The tb1 gene controls the plant's branching architecture, with the domesticated version of tb1 leading to fewer branches and a single, large central stalk, which supports a larger ear (Doebley et al., 1995). This change made maize more suitable for cultivation and harvesting. Another significant gene, teosinte glume architecture1 (tga1), influenced the development of the maize kernel's protective casing. The domesticated allele of tga1 led to the reduction of the hard glumes that enclose the kernels in teosinte, resulting in the "naked" kernels of maize that are easily accessible (Wang et al., 2005). In addition to these genetic changes, the domestication process also involved alterations in the plant's reproductive structures. The transformation of the inflorescence from a teosinte-like structure to the modern maize ear involved changes in the expression and regulation of multiple genes, leading to the development of female ears on the central stalk and male tassels at the top (Doebley et al., 1990). The domestication of maize also involved metabolic changes. Comparative metabolomics studies have shown that domesticated maize and teosinte have distinct metabolic profiles, with maize having adapted to different
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