Rice Genomics and Genetics 2025, Vol.16, No.4, 219-236 http://cropscipublisher.com/index.php/rgg 219 Feature Review Open Access Regulation of Starch Biosynthesis Pathway for Improved Grain Quality in Rice Chengxi Wang, Xinguang Cai, Qiangsheng Qian Modern Agricultural Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China Corresponding email: qiangsheng.qian@cuixi.org Rice Genomics and Genetics, 2025, Vol.16, No.4 doi: 10.5376/rgg.2025.16.0019 Received: 16 Jun., 2025 Accepted: 29 Jul., 2025 Published: 16 Aug., 2025 Copyright © 2025 Wang 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: Wang C.X., Cai X.G., and Qian Q.S., 2025, Regulation of starch biosynthesis pathway for improved grain quality in rice, Rice Genomics and Genetics, 16(4): 219-236 (doi: 10.5376/rgg.2025.16.0019) Abstract The quality of rice mainly depends on the composition and structure of starch within its grains. The ratio of amylose to amylopectin content not only affects the steamed and cooked taste quality and nutritional value of rice, but also relates to the digestibility and glycemic index of rice and other health attributes. To meet the growing demand for high-quality rice, it is of great significance to conduct in-depth research on the molecular basis of starch biosynthesis in rice grains. This study reviews the biochemical mechanisms, genetic regulatory networks, and molecular breeding strategies of the rice starch synthesis pathway, introduces the functions and expression patterns of the main enzymes and related genes in starch synthesis during grain development, and summarizes the regulatory effects of transcription factors, non-coding Rnas, and epigenetic modifications on starch synthesis. This paper analyzes the key genetic loci and alleles that affect the ratio of amylose to amylopectin and the structure of starch grains. Combined with the research cases of typical gene mutants, it explores the strategies for improving the quality of rice grains through molecular breeding methods, including the application of new technologies such as molecular marker-assisted selection and gene editing. This study summarizes the latest progress in the regulation of starch synthesis, looks forward to its application prospects in the cultivation of high-quality rice in the future, and provides theoretical support and feasible molecular improvement strategies for the breeding of high-quality rice. Keywords Rice; Starch synthesis; Amylose; Genetic regulation; Grain quality 1 Introduction The main component of rice is starch, which accounts for approximately 80% of the dry weight of the grains. There are two types of starch: amylose and amylopectin. Their proportion will directly affect the taste and nutrition of the rice. Generally speaking, rice with a high content of amylose tends to have harder grains when cooked and dries out easily when cooled. Rice with less amylose and more amylopectin is more sticky and soft when cooked and tastes more glutinous. For instance, glutinous rice is almost entirely amylopectin and becomes very sticky when cooked. Indica rice with more than 25% amylose will be dry and hard when cooked. The composition of starch can also affect the digestion speed of rice. When there is a high amount of amylose, more resistant starch will be produced, which can lower the glycemic index of rice and be more friendly to diabetic patients. Apart from starch, the protein content and types in the grains also affect the texture and flavor of the rice. The composition of starch is a key factor determining the quality and nutrition of rice. Optimizing it not only makes the taste better but also meets people's demand for health. Nowadays, people's living standards have improved, and their demands for the quality of rice are also getting higher and higher. In the past, breeding mainly focused on yield and paid insufficient attention to the improvement of rice quality, so there were not many high-quality rice varieties. The current challenge lies in how to ensure the output while making the rice taste better and more nutritious. The synthesis process of starch directly determines the amylose content, gel consistency and gelatinization characteristics of rice, all of which are important indicators affecting the quality of rice. Studying the biochemical processes and genetic regulation of starch synthesis can identify the key genes and their modes of action that affect rice quality, providing theoretical support for molecular breeding. For instance, the Wx gene controls the synthesis of amylose. Its different alleles can cause significant differences in the amylose content of rice, which is also one of the important reasons for the taste differences between indica rice and japonica rice (Huang et al., 2020). For instance, if the enzymes that regulate
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