Lysine and tryptophan are two essential amino acids and these are deficit in maize grain thus posing the problem of nutritional deficiencies in the consumers. A wide range of deficiency symptoms like cognitive disorder, kwashiorkor disease, reduced appetite, impaired skeleton development, delayed growth and aberrant behaviour are associated with lysine and tryptophan deficiency. These amino acids are also important to cure the Pellagra disease. Researchers identified several mutants in maize especially opaque-2 which are responsible for higher lysine and tryptophan contents. Few years later, it was observed that opaque-2 mutant has several pleiotropic effects on maize grain and plant. Efforts of researchers are spanning over the period of four decades to develop quality protein maize (QPM). QPM is described as nutritionally superior maize with high lysine and tryptophan contents and desired kernel characteristics as compared to its normal maize counterparts. Biological value of QPM was almost equivalent to egg protein. Breeding of maize for quality protein is based on three genetic systems like opaque-2 genetic system, endosperm modifier genetic system and associated gene systems. Keeping in view the importance of QPM, current review article is compiled to discuss the genetic basis, genetic systems and breeding strategies. Timeline for various events is also drafted like discovery of various mutants, several conventional and modern approaches for development and deployment of QPM varieties across the world. Despite its nutritional benefits, the rate of adoption of QPM is generally at low pace in the developing world and this review article discuss the challenges and potential opportunities for QPM adoption.

中文翻译：

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优质蛋白玉米 (QPM)：重要性、遗传学、不同事件的时间线、育种策略和品种采用

赖氨酸和色氨酸是两种必需氨基酸，它们在玉米粒中缺乏，从而造成消费者营养缺乏的问题。广泛的缺乏症状，如认知障碍、kwashiorkor 病、食欲下降、骨骼发育受损、生长迟缓和行为异常，都与赖氨酸和色氨酸缺乏有关。这些氨基酸对于治愈糙皮病也很重要。研究人员在玉米中发现了几种突变体，尤其是 opaque-2，它们负责更高的赖氨酸和色氨酸含量。几年后，观察到 opaque-2 突变体对玉米籽粒和植物具有多种多效性。研究人员的努力跨越了四个十年的时间来开发优质蛋白质玉米 (QPM)。QPM 被描述为具有高赖氨酸和色氨酸含量以及与其正常玉米对应物相比所需的籽粒特性的营养优良玉米。QPM的生物学价值几乎与鸡蛋蛋白相当。优质蛋白质玉米育种基于三个遗传系统，如 opaque-2 遗传系统、胚乳修饰基因系统和相关基因系统。考虑到 QPM 的重要性，现编制综述文章以讨论遗传基础、遗传系统和育种策略。还起草了各种事件的时间表，例如发现各种突变体、几种用于在世界范围内开发和部署 QPM 品种的传统和现代方法。尽管营养丰富，