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OsMADS1 plays a vital role in regulating floret development and grain shape, but whether it regulates rice grain quality still remains largely unknown. Therefore, we used comprehensive molecular genetics, plant biotechnology, and functional omics approaches, including phenotyping, mapping-by-sequencing, target gene seed-specific RNAi, transgenic experiments, and transcriptomic profiling to answer this biological and molecular question. Here, we report the characterization of the 'Oat-like rice' mutant, with poor grain quality, including chalky endosperms, abnormal morphology and loose arrangement of starch granules, and lower starch content but higher protein content in grains. The poor grain quality of Oat-like rice was found to be caused by the mutated OsMADS1Olr allele through mapping-by-sequencing analysis and transgenic experiments. OsMADS1 protein is highly expressed in florets and developing seeds. Both OsMADS1-eGFP and OsMADS1Olr-eGFP fusion proteins are localized in the nucleus. Moreover, seed-specific RNAi of OsMADS1 also caused decreased grain quality in transgenic lines, such as the Oat-like rice. Further transcriptomic profiling between Oat-like rice and Nipponbare grains revealed that OsMADS1 regulates gene expressions and regulatory networks of starch and storage protein metabolisms in rice grains, hereafter regulating rice quality. In conclusion, our results not only reveal the crucial role and preliminary mechanism of OsMADS1 in regulating rice grain quality but also highlight the application potentials of OsMADS1 and the target gene seed-specific RNAi system in improving rice grain quality by molecular breeding. [ABSTRACT FROM AUTHOR]

High yield and superior quality are the main objectives of rice breeding and research. While innovations in rice breeding have increased production to meet growing demand, the universal issue of balancing high yield and susperior quality has led to a lack of focus on improving rice quality. With rising living standards, improving rice quality has become increasingly important. Rice grain quality is a complex trait influenced by both genetic and environmental factors, with four primary aspects: milling quality, appearance quality, eating and cooking quality, and nutritional quality. While different populations have varying demands for rice quality, the core traits that contribute to rice quality include grain shape and chalkiness in terms of appearance, as well as endosperm composition that influences cooking and sensory evaluation. Researchers have made substantial advancements in discovering genes/QTLs associated with critical traits including appearance, aroma, texture, and nutritional properties. Markers derived from these genetic discoveries have provided an efficient tool for marker-assisted selection to improve rice quality. Thus, this review focuses on elite genes and their applications in breeding practices to quickly develop superior quality rice varieties that meet various market demands. [ABSTRACT FROM AUTHOR]

The source strength and sink demand as well as their interaction have been demonstrated to co-regulate the synthesis of starch and determine the grain quality, but the knowledge of the underlying physiological mechanisms is limiting. An indica variety, Yangdao 6, and a japonica variety, Jinxiangyu 1, were planted with three treatments, including normal growth plant (CK), leaf-cutting (LC) and spikelet-thinning (ST). The transcript levels of starch metabolic genes, physicochemical characteristics of starch and appearance, milling, cooking and tasting qualities of rice under different treatments were determined. The ST treatment increased the relative expression of genes related to the synthesis of short branch-chains of amylopectin (SSI, BEI, BEIIb) and amylose (GBSSI) and reduced the relative expression of medium-long to long branch-chains of amylopectin synthesis genes (SSIIa, SSIIIa, SSIIIb, ISA1). When comparing ST with the CK treatment, starch granules became smoother with higher contents of short branch-chains and lower ratios of medium-long and long branch-chains of amylopectin; the crystallinity and the value of 1045/1022 cm−1 was decreased; for pasting properties, the setback and pasting temperature were decreased; the peak viscosity, hot viscosity, breakdown and final viscosity were significantly increased. Meanwhile, the ST treatment improved the appearance, milling and cooking and tasting qualities. The opposite results were observed under the LC treatment. These results indicated that source strength and sink size would regulate expression levels of starch metabolic genes, which is pivotal for the contents of amylose and short/long branch chains ratio of amylopectin, thus changing the structure and physicochemical properties of starch and grain quality. Here, we speculated that the improved source strength in terms of higher leaf/canopy photosynthesis and small sink size, such as small panicle size, would be preferred traits in high grain quality rice breeding. [ABSTRACT FROM AUTHOR]

Grain quality has become one of the foci in rice breeding worldwide since it is crucial for farmers, millers and consumers. Previous studies have revealed that rice gain quality is mainly determined with several major characteristics including milling, physical appearance, eating and cooking, sensory and nutritional value. In genetics, rice grain quality is a complex trait controlled by polygene/QTL. Better understanding the mechanism underlying the grain quality is fundamental for developing new breeding strategies. Therefore, abundant studies had been conducted to discover the factors that control the quality traits, and led to dozens of QTL identified and several major genes cloned. This has enabled development of the functional markers to facilitate selection of the complex traits. But breeding for rice varieties with desired grain quality needs to pyramid multiple and beneficial loci or alleles, some of which are still untapped. In this chapter, we first summarize the literatures on rice grain quality traits and the relevant phenotyping approaches, and then review the progress in genetic dissection of these traits. This review also presented the breeding attempts using marker-assisted selection, genomics-assisted breeding approaches, as well as genome editing technologies, and finally provided innovative insights into the future of rice grain quality breeding by using the modern technology with integration of machine learning and genomic selection. [ABSTRACT FROM AUTHOR]

The determination of rice grain quality (RGQ) parameters is important because it is the benchmark of rice breeding success to meet up the consumers' demand. RGQ includes milling, storage, cooking, eating, nutrition, and market quality of rice grain. Furthermore, demand for high-quality rice has increased globally and is expected to continue to rise due to consumer preferences. However, global consumer demand, culture, and demographic variances determine acceptable RGQ attributes. For example, European consumers prefer long-grain, nonaromatic rice, whereas Middle Eastern consumers prefer long-grain, well-milled rice with a strong aroma. To improve the rice quality, RGQ analysis is the best way; besides we need to understand the genetic mechanism of the several grain quality quantitative trait loci (QTLs) actions. A better understanding of these QTLs can be tremendously useful in the development of novel RGQ varieties. This review is intended to study major RGQ parameters and their assessment tools. This study is focusing on the limitations and prospects of QTLs to improve RGQ. [ABSTRACT FROM AUTHOR]

Rice is the most staple food consuming in China. During the past six decades, a large number of indica inbred rice cultivars have been developed. However, seldom studies have focused on evaluating the dynamic changes of grain quality improvement among the major cultivars. Our study evaluated the genetic improvement of 12 quality traits in indica inbred rice cultivars developed in rice breeding programs in South China during 1956–2020. The results indicated that significant improvement had been gained for the appearance quality, cooking and eating quality in the breeding program since the 1990s, while slight genetic improvement was attained before 1990. Among all the 12 traits, MGL (Milled Grain Length), LWR (Length Rate Ratio), GC (Gel Consistency), and ASV (Alkali Spreading Value) were significantly increased among these different cultivars; MGW (Milled Grain Width), CGR (Chalky Grain Rate), CA (Chalkiness Area), and AC (Amylase Content) showed a tremendously decreased trend from last thirty years. However, the other four traits, such as BRR (Brown Rice Rate), MRR (Milled Rice Rate), HMRR (Head Milled Rice Rate), and PC (Protein Content) showed little improvement during the breeding processes in these cultivars. The results also suggested that selecting a slender grain shape would be beneficial for breeding high quality indica rice. We also discussed that improving milling quality, especially HMRR of the high-quality cultivars and nutrition quality for special consumer groups as an meaningful direction for rice breeding. [ABSTRACT FROM AUTHOR]

Grain qualities including milling quality, appearance quality, eating and cooking quality, and nutritional quality are important indicators in rice breeding. Significant achievements in genetic improvement of rice quality have been made. In this study, we analyzed the variation patterns of 16 traits in 1570 rice varieties and found significant improvements in appearance quality and eating and cooking quality, particularly in hybrid rice. Through genome-wide association study and allelic functional nucleotide polymorphisms analysis of quality trait genes, we found that ALK , FGR1 , FLO7 , GL7 / GW7 , GLW7 , GS2 , GS3 , ONAC129 , OsGRF8 , POW1 , WCR1 , and Wx were associated with the genetic improvement of rice quality traits in Southern China. Allelic functional nucleotide polymorphisms analysis of 13 important rice quality genes, including fragrance gene fgr , were performed using the polymerase chain reaction amplification refractory mutation system technology. The results showed that Gui516, Gui569, Gui721, Ryousi, Rsimiao, Rbasi, and Yuehui9802 possessed multiple superior alleles. This study elucidates the phenotypic changes and molecular basis of key quality traits of varieties in Southern China. The findings will provide guidance for genetic improvement of rice quality and the development of new varieties. • Appearance quality (AQ) and eating and cooking quality (ECQ) • ALK , FGR1 , FLO7 , GL7 / GW7 , GLW7 , GS2 , GS3 , ONAC129 , OsGRF8 , POW1 , WCR1 , and Wx are the main genes affecting rice quality in Southern China. • Gui516, Gui569, Gui721, Ryousi, Rsimiao, Rbasi, and Yuehui9802 possessed multiple superior alleles of rice quality. [ABSTRACT FROM AUTHOR]

‘Yechan’ is a high grain quality mid-late maturing rice cultivar with lodging tolerance and multiple disease resistance. It was a derived from a cross between ‘Hopum’ and ‘Iksan537’ (cultivar name ‘Haepum’). ‘Hopum’ is a high grain quality mid-late maturing rice cultivar with strong lodging tolerance and ‘Haepum’ is a high grain quality medium maturing rice cultivar with multiple disease resistance. To shorten the breeding period, another culture method was applied to the F1 plants. ‘Yechan’ was selected through the pedigree method, yield trials, and local adaptability tests, with a high selection pressure for grain quality, lodging, and disease resistance. The heading date of ‘Yechan’ was August 14, one day later than that of ‘Nampyeong’. ‘Yechan’ is a cultivar tolerant to lodging and it has short culms. It has multiple disease resistance against rice blast, rice stripe virus, and bacterial blight, including the K3a race, the most virulent race in Korea. The yield of ‘Yechan’ was similar to that of ‘Nampyeong’. ‘Yechan’ showed excellent grain appearance, superior taste when cooked, and enhanced milling performance; thus, we concluded that it could contribute to the improvement of Korean japonica rice cultivar quality. ‘Yechan’, a high grain quality mid-late maturing rice cultivar with lodging tolerance and multiple disease resistance, would be suitable for cultivation in the southern plain area in Korea and has been utilized in the breeding programs aimed at enhancing the grain quality and stability for the cultivation of Korean japonica rice (Registration No. 7647). [ABSTRACT FROM AUTHOR]

High-quality rice varieties are planted widely in southern China. However, the changes in grain quality in the different high-quality rice varieties released in recent years are unclear. This study compared the grain quality changes and status of those varieties and presented proposals for future breeding. In the past 11 years, high-quality indica has significantly improved chalky rice rate (CRR), chalkiness degree (CD) but decreased head rice rate (HRR); amylose content (AC), gel consistency (GC) and length-to-width ratio (LWR) were improved only in indica hybrid rice. Most high-quality rice varieties grown in southern China are primarily indica rice. In contrast to indica rice, japonica rice had increased milling recovery, cooking and eating qualities (CEQ), but worsened significantly the physical appearance. For japonica rice, hybrid varieties exhibited a marked improvement in the rice quality for lower AC, higher GC and LWR compared with inbred varieties. A higher grain quality was observed in inbred varieties for indica rice due to lower CRR, CD and AC, higher HRR and GC. Our results suggested that we should be focused on improving the physical appearance quality for japonica rice and milling recovery, particularly CEQ for indica rice, for future high-quality rice breeding. • High-quality indica rice has significantly improved chalky rice rate and degree of chalkiness over time. • High-quality japonica rice had increased milling recovery and CEQ compared with high-quality indica rice. • High-quality japonica hybrid rice significantly improved grain quality and that was observed in indica inbred rice. [ABSTRACT FROM AUTHOR]

Anther/pollen culture technology is being efficiently used for accelerating rice breeding progress and improving grain quality characters. Using pollen culture technique, we obtained elite rice (Oryza sativa L.) line DHP6, which is well adapted to the highlands of Madagascar. Here we show that certain grain, nutritional, and culinary quality characteristics have been significantly improved in line DHP6. Morphometric and physico-chemical analysis demonstrated that physical (colour, transluscency, and chalkiness), chemical (amylose content, alkali spreading value, and gel consistency) and cooking (volume expansion, elongation ratio) features were greatly improved compared to the parental line. Culinary and nutritional quality analyses showed a significant increase in nutritional values and mineral richness. Some desired concentrations of minerals like Mg and Cu were much higher (e.g. three times richer in Cu) than those of its parental line (variety IR58614). Taken together, such ameliorated grain quality traits will promote its wide-scale planting by the farmers and should thus help to improve the nutritional quality of the population of Madagascar. [ABSTRACT FROM AUTHOR]

To ensure rice food security, the target outputs of future rice breeding programmes should focus on developing climate-resilient rice varieties with emphasis on increased head rice yield coupled with superior grain quality. This challenge is made greater by a world that is increasingly becoming warmer. Such environmental changes dramatically impact head rice and milling yield as well as increasing chalkiness because of impairment in starch accumulation and other storage biosynthetic pathways in the grain. This review highlights the knowledge gained through gene discovery via quantitative trait locus (QTL) cloning and structural-functional genomic strategies to reduce chalk, increase head rice yield, and develop stable lines with optimum grain quality in challenging environments. The newly discovered genes and the knowledge gained on the influence of specific alleles related to stability of grain quality attributes provide a robust platform for marker-assisted selection in breeding to design heat-tolerant rice varieties with superior grain quality. Using the chalkiness trait in rice as a case study, we demonstrate here that the emerging field of systems genetics can help fast-track the identification of novel alleles and gene targets that can be pyramided for the development of environmentally robust rice varieties that possess improved grain quality. [ABSTRACT FROM AUTHOR]

The eating and cooking qualities of rice grains are the major determinants of consumer preference and, consequently, the economic value of a specific rice variety. These two qualities are largely determined by the physicochemical properties of the starch, i.e. the starch composition, of the rice grain. In our study, we determined the genetic factors responsible for the physicochemical properties of starch in recombinant inbred lines (RILs) of japonica cv. Tainung 78 × indica cv. Taichung Sen 17 (TCS 17) cultivated over two crop seasons by examining palatability characteristics and several Rapid Viscosity Analyzer (RVA) parameters. Thirty-four quantitative trait loci (QTLs), each explaining between 1.2 and 78.1 % phenotypic variation, were mapped in clusters on eight chromosomes in 190 RILs genotyped with 139 markers. Ten pairs of QTLs were detected in the two environments, of which seven were in agreement with previous findings, suggesting that these QTLs may express stable experimental populations across various environments. Waxy ( Wx), which controls amylose synthesis, was determined to be a primary gene regulating the physicochemical properties of cooked rice grains, as indicated by the presence of a major QTL cluster on chromosome 6 and by marker regression analysis. Six starch synthesis-related genes (SSRGs) which were located in the QTL intervals significantly differed in terms of gene expression between the two parents during grain-filling and were important genetic factors affecting physicochemical properties. The expression of four genes, PUL, ISA2, GBSSI, and SSII- 3, was significantly upregulated in TCS 17, and this expression was positively correlated with six traits. The effects of the six SSRGs and gene interaction depended on genetic background and environment; grain quality may be fine tuned by selecting for SBE4 for japonica and PUL for indica. We provide valuable information for application in the breeding of new rice varieties as daily staple food and for use in industrial manufacturing by marker-assisted selection. [ABSTRACT FROM AUTHOR]