Molecular Plant Breeding 2025, Vol.16, No.1, 93-104 http://genbreedpublisher.com/index.php/mpb 93 CaseStudy Open Access Case Study: Breeding Maize Varieties with High Protein Content Qiaohong Ying, Qiong Chen, Kaozu Lei, Huazhou Liu Zhejiang Kecheng Seed Industry Co., Ltd., Wenzhou, 325019, Zhejiang, China Corresponding email: keseed@qq.com Molecular Plant Breeding, 2025 Vol.16, No.1 doi: 10.5376/mpb.2025.16.0010 Received: 19 Jan., 2025 Accepted: 21 Feb., 2025 Published: 28 Feb., 2025 Copyright © 2025 Ying et al., This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Ying Q.B., Chen Q., Lei K.Z., and Liu H.Z., 2025, Case study: breeding maize varieties with high protein content, Molecular Plant Breeding, 16(1): 93-104 (doi: 10.5376/mpb.2025.16.0010) Abstract This study gives an account of the breeding efforts of high-protein maize varieties, particularly Quality Protein Maize (QPM), and their potential to address malnutrition and improve the nutritional value of maize. Compared to conventional maize, QPM varieties contain higher levels of essential amino acids such as lysine and tryptophan, which are crucial for human and animal nutrition. Research has shown that the adoption of QPM significantly improves children's growth, indicating its potential to combat malnutrition in developing regions. However, QPM breeding still faces challenges, such as reduced yield and insufficient agronomic traits. Future research directions include integrating molecular breeding with conventional methods, exploring genetic loci associated with protein synthesis and stress tolerance, and developing QPM varieties that are both nutritionally superior and agronomically viable. Keywords High-protein maize; Quality protein maize (QPM); Malnutrition; Molecular breeding; Essential amino acids 1 Introduction As one of the three most widely grown cereal grains globally, maize plays a foundational role in the diets of millions. Accounting for approximately 15% of global protein intake and 20% of calories in many developing countries, maize has a unique position among staple crops for its calorie density and relative ease of production (Zarkadas et al., 1995). Its flexibility in various climates, from temperate to tropical zones, allows it to thrive where other crops may not, increasing its importance in food and feed systems globally (Denic et al., 2012). However, conventional maize varieties have limited amino acid profiles, which are deficient in lysine and tryptophan, reducing their overall biological value when consumed as a primary protein source. Enhancing the protein content and quality of maize would address a significant nutritional gap. Conventional maize varieties are often low in essential amino acids such as lysine and tryptophan, leading to protein deficiency risks in populations heavily reliant on maize as a staple (Bhatnagar et al., 2004). Quality Protein Maize (QPM), developed to address these gaps, demonstrates superior nutritional value by offering a more complete amino acid profile, critical for both human health and animal feed efficiency. This biofortification effort not only raises the nutritional profile of the maize grain but also contributes to reducing health issues related to protein deficiency in vulnerable populations, particularly in developing countries (Tandzi et al., 2017). Breeding high-protein maize varieties presents a range of challenges and opportunities. Key challenges include maintaining crop yield while improving protein content, ensuring genetic diversity, and achieving resilience to environmental stressors. Recent advances in molecular breeding techniques have allowed researchers to identify and target genes associated with enhanced protein levels and amino acid profiles. For example, genetic modification efforts have introduced markers like the opaque-2 gene to help enhance lysine and tryptophan levels (Vasal, 2014). Traditional and molecular breeding methods alike continue to develop hybrids capable of maintaining nutritional value under variable conditions, such as low soil nitrogen or drought (Bello et al., 2014). These ongoing efforts to produce QPM varieties highlight the balancing act between enhancing protein quality and managing the practical limitations of crop performance. This study aims to synthesize current research efforts in high-protein maize breeding, highlighting advancements in genetic selection, breeding methodologies, and the challenges faced in real-world application. It also seeks to
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