Molecular Plant Breeding 2024, Vol.15, No.5, 282-294 http://genbreedpublisher.com/index.php/mpb 285 4.2 Transgenic technologies: incorporation of foreign genes into maize genomes Transgenic technologies involve the introduction of foreign genes into the maize genome to confer new traits. This method has been instrumental in developing maize varieties with improved characteristics such as pest resistance, herbicide tolerance, and enhanced nutritional content. The process typically involves the use of Agrobacterium-mediated transformation or biolistic (gene gun) methods to insert the desired genes into the maize DNA. These transgenic approaches have significantly contributed to the advancement of maize breeding by enabling the incorporation of beneficial traits from other species (Svitashev et al., 2015; Chen et al., 2019; Távora et al., 2022). 4.3 RNA interference (RNAi) for gene silencing in maize RNA interference (RNAi) is a powerful technique for gene silencing that involves the use of small RNA molecules to downregulate the expression of specific genes. In maize, RNAi has been utilized to suppress genes responsible for undesirable traits, thereby improving crop performance. This method allows for the targeted regulation of gene expression without altering the overall genome structure. RNAi has been particularly effective in enhancing resistance to pests and diseases, as well as improving stress tolerance and yield in maize (Rajput et al., 2021; Távora et al., 2022). 4.4 Applications of synthetic biology in maize breeding Synthetic biology combines principles from engineering and biology to design and construct new biological parts, devices, and systems. In maize breeding, synthetic biology approaches have been used to create novel genetic circuits and pathways that can enhance crop traits. This includes the development of synthetic promoters, regulatory elements, and metabolic pathways to improve photosynthesis, nutrient use efficiency, and stress resilience. The integration of synthetic biology with traditional breeding and modern gene-editing techniques holds great promise for the future of maize breeding, enabling the creation of highly optimized and resilient crop varieties (Chen et al., 2019; Lorenzo et al., 2022; Ahmad, 2023). By leveraging these advanced genetic engineering techniques, researchers and breeders can accelerate the development of maize varieties that meet the growing demands for food security and sustainable agriculture. 5 Enhancing Agronomic Traits Through Genetic Engineering 5.1 Improving yield potential and stability Genetic engineering has significantly contributed to improving the yield potential and stability of maize. By integrating advanced biotechnological approaches, such as transgenic technology and genome editing, researchers have been able to introduce genes that enhance yield under various environmental conditions. For instance, the discovery and field testing of over 3 331 DNA cassette constructs by Corteva Agriscience™ led to the identification of at least 22 validated gene leads that improved yield in elite maize breeding germplasm (Simmons et al., 2021). Additionally, the integration of doubled haploidy, high-throughput phenotyping, and genomics-assisted breeding has been crucial in developing elite maize cultivars with enhanced yield potential and stability, particularly in stress-prone environments (Prasanna et al., 2021). 5.2 Enhancing resistance to biotic stresses: pests and diseases The development of maize varieties with enhanced resistance to biotic stresses, such as pests and diseases, is a critical aspect of genetic engineering. The International Maize and Wheat Improvement Center (CIMMYT) has been at the forefront of breeding maize with tolerance to key biotic stresses, deploying elite stress-tolerant maize cultivars across various regions (Figure 2) (Prasanna et al., 2021). Moreover, the identification and manipulation of stress-related genes through transgenic technology have led to the generation of maize plants with improved resistance to pests and diseases, thereby securing food production in the face of biotic challenges (Esmaeili et al., 2022). 5.3 Developing drought-tolerant and abiotic stress-resistant maize varieties Drought tolerance and resistance to other abiotic stresses are vital traits for ensuring maize productivity in the face of climate change. Genetic engineering has played a pivotal role in developing drought-tolerant maize varieties. For example, the genetic dissection of drought tolerance through linkage and association mapping has provided
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