Starch serves as a crucial storage substance in both cereal crops and root/tuber crops, with its composition and properties determining the quality of storage organs. The Waxy (Wx) gene, encoding a key enzyme in starch biosynthesis, plays a pivotal role in this metabolic pathway. However, existing reviews seldom systematically elaborate on Wx gene regulatory mechanisms from the perspective of intrinsic molecular networks. Focusing on the model crop rice, this article synthesizes research advances in Wx-mediated starch biosynthesis regulation over the past decade. We analyze the structural features of the Wx gene and factors influencing its regulatory function during starch synthesis. In conclusion, future research directions are proposed to provide references for Wx gene studies in other crops, as well as theoretical foundations for rice varietal improvement and molecular design breeding.

Rice is one of the world's most abundant food crops. The amylose content is a key factor affecting the production of high-quality rice. The commonly used method for determining the amylose content is the Iodine-Starch colorimetric method. Due to the limitations of traditional iodine colorimetric methods, this experiment provides a simple high-throughput method (SSDM) for determining amylose content. Using rice varieties with different genetic backgrounds as experimental materials, the accuracy and practicality of the new method were explored to improve measurement efficiency and simplify the operation process. The results demonstrated a strong correlation (R = 0.9998) between the absorbance values and amylose content, with a relative deviation of less than 1.2%. It showed good repeatability, with a variation range of 0.43% to 1.63%. The experiment takes a short time and can measure 96 samples at once. Therefore, while ensuring the accuracy of experimental results, the high-throughput measurement method improves the efficiency of measuring amylose content. This has important practical significance for early screening and identification of excellent individuals in rice quality genetic breeding programs.

Hybrid rice technology has been used for more than 50 years, and eating and cooking quality (ECQ) has been a major focus throughout this period. Waxy (Wx) and alkaline denaturation (ALK) genes have received attention owing to their pivotal roles in determining rice characteristics. However, despite significant effort, the ECQ of restorer lines (RLs) has changed very little. By contrast, obvious changes have been seen in inbred rice varieties (IRVs), and the ECQ of IRVs is influenced by Wx, which reduces the proportion of Wxa and increases the proportion of Wxb, leading to a decrease in amylose content (AC) and an increase in ECQ. Meanwhile, ALK is not selected in the same way. We investigated Wx alleles and AC values of sterile lines of female parents with the main mating combinations in widely used areas. The results show that almost all sterile lines were Wxa-type with a high AC, which may explain the low ECQ of hybrid rice. Analysis of hybrid rice varieties and RLs in the last 5 years revealed serious homogenisation among hybrid rice varieties.

Six rice cultivars with similarly high amylose contents but significant differences in resistant starch (RS) contents were employed to investigate factors affecting rice starch digestibility. Results of scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction analyses revealed that the enzymolysis resistance and high gelatinization temperature (GT) of the starch granules were the main reasons for the different starch digestibilities. Furthermore, starch fine structure analysis showed that RS content has a positive correlation with intermediate chain amylopectin (DP 13-24) content and a negative correlation with short chain amylopectin (DP 6-12) content. Moreover, under normal cooking conditions, some starch granules within the endosperm do not gelatinize completely due to the high GT of the starch, leading to a lower starch digestibility. Overall, this work provides useful information for understanding the effects of starch fine structure as well as GT on starch digestibility.

Rice grain quality is a complex trait that includes processing, appearance, eating, cooking, and nutrition components. The amylose content (AC) in the rice endosperm affects the eating and cooking quality along with the appearance of milled rice. In this study, four indica rice varieties with different ACs were used to study the factors affecting endosperm transparency along with the physical and chemical characteristics and eating quality of translucent endosperm varieties. Endosperm transparency was positively correlated with water content and negatively correlated with the cumulative area of cavities within starch granules. The indica landrace 28Zhan had a translucent endosperm and exhibited good taste. Based on starch fine structure analysis, long-chain amylopectin and the B2 chain of amylopectin might be major contributors to the good taste and relatively slow digestion of this landrace.

以4个具有相似的高直链淀粉含量水稻品种为试验材料,分析其淀粉和米粉的消化特性以及影n向消化特性的因素.结果 表明:相对于其他2个品种,MRX和ZXM的米粉和淀粉的酶解消化程度最低;所有品种水稻基本理化特性如表观直链淀粉含量、胶稠度、总淀粉以及蛋白质含量等对淀粉的消化特性无实质影响;不同品种间淀粉消化特性差异主要是由淀粉粒的结构差异引起的,MRX和ZXM淀粉粒在酶解消化过程中较为稳定,不易被酶侵蚀而破碎;其糊化温度和热焓值均显著高于其他2个品种,可能与其支链淀粉具有较高比例的短支链(DP 12-24)有关.

以携带相同Wxb基因的籼稻品种黄华占和扬稻6号为试验材料,系统分析了这2个优质籼稻品种的理化特性和淀粉精细结构.结果表明,黄华占稻米蛋白质含量显著低于扬稻6号,而表观直链淀粉含量高于扬稻6号,其他理化品质如胶稠度、总淀粉含量和碱消值两者无显著差异;黄华占稻米具有较高的糊化温度和热焓值.黄华占和扬稻6号稻米淀粉粘滞曲线较为接近,但黄华占稻米具有较高的崩解值和较小的回复值.扫描电镜分析表明,淀粉粒形态和结构在2个样品间无明显差异;但淀粉精细结构分析表明,黄华占稻米淀粉含有较少的支链淀粉短链以及较多的支链长链和较多的直链淀粉短链;淀粉晶体结构分析表明,黄华占和扬稻6号淀粉均为A型晶体,但黄华占稻米淀粉的长程有序结构较扬稻6号淀粉高,而短程有序结构样品间无显著差异.上述研究为选育优质籼稻提供了参考.

The gelatinization temperature (GT) of endosperm starch influences rice eating and the cooking quality (ECQ). ALK encoding soluble starch synthase IIa (SSIIa) is the major gene determining grain GT in rice. Herein, we identified a spontaneous ALK mutant named ALK(d), which resulted from a G/T single-nucleotide polymorphism (SNP) in exon 1 of the ALK(c) allele from the high-GT indica rice cultivar. Compared with grains from the ALK(c) near-isogenic line (NIL), NIL(ALK(d)) grains exhibited a high GT (2.3 degrees C) and improved retrogradation properties. The NIL(ALKa) grain starch contained an increased proportion of amylopectin intermediate chains (DP 13-24) at the expense of short chains (DP < 12), resulting in enhancements in both the crystallinity and the lamellar peak intensity compared with low-GT rice grains. Moreover, both NIL(ALK(d)) and NIL(ALK) grains also featured a significantly lower apparent amylose content (AAC), harder gel consistency (GC), higher pasting curve, and poorer taste values in comparison to Nip(ALK(d)) grains. Taken together, this work provides novel insights underlying the allelic variation of the ALK gene in rice.