Susong Zhu

Fragrant rice is regarded as a premium variety due to its distinctive aroma, delicate texture, and rich nutritional value. This aroma primarily originates from 2-acetyl-1-pyrroline (2-AP), but the metabolic basis of 2-AP remains elusive to this day, and the genetic basis for metabolite accumulation is largely unknown. While several researchers have investigated differences in 2-AP synthesis pathways between fragrant and non-fragrant rice, few studies have examined the 2-AP synthesis pathways in fragrant rice varieties exhibiting 2-AP differences. Therefore, after conducting gene similarity analyses on six fragrant rice varieties, we measured the expression levels of substances and related genes involved in multiple metabolic pathways within the 2-AP synthesis pathway, along with the specific enzyme activities associated with these pathways. Results indicate that XG12 (Guizhou Fragrant Rice Variety) exhibits the highest 2-AP content, yet its efficiency in synthesizing 2-AP is not the highest across any individual metabolic pathway. This finding reveals that among fragrant rice varieties, 2-AP content negatively correlates with OsBadh2 expression levels and GABA content, while showing no linear correlation with other related substances or metabolic genes. At this point, variations in the major effect gene OsBadh2 no longer dominate; instead, subtle differences in 2-AP content are jointly determined by numerous minor effect genes and environmental factors. This phenomenon not only resolves apparent contradictions but profoundly illuminates the complex regulatory mechanisms governing 2-AP biosynthesis. 2-AP synthesis represents a dynamic equilibrium process, with different fragrant rice varieties potentially accumulating 2-AP through distinct metabolic pathways. Additionally, this study analyzed the volatile organic compounds (VOCs) of six fragrant rice varieties through metabolomics. Results revealed that DLX, which exhibited the lowest 2-AP content, contained the richest array of aggregated VOCs, indicating no correlation between 2-AP and numerous VOCs. Our findings provide a clear research direction for elucidating the genetic regulatory mechanisms of 2-AP underlying fragrant rice and lay the foundation for technological research aimed at enhancing the aroma of fragrant rice varieties.

In addition to being governed by genetic factors, environmental factors also play a crucial role in influencing the fragrance of rice. In this research, the high-quality rice variety Dalixiang was selected as the experimental material to investigate the impacts of soil nutrients in Guiyang and Meitan on its fragrance. The results indicated that the levels of ammonium nitrogen, organic matter, total nitrogen, available nitrogen, and the pH value in the soil of Meitan were lower compared to those in Guiyang. Conversely, the contents of total potassium, available phosphorus, and available potassium were higher in Meitan. Specifically, the concentrations of 2-acetyl-1-pyrroline (2AP) in the leaves of Dalixiang at the heading stage and in the grains at the maturity stage at the Meitan planting site were 0.13 mg/kg and 0.56 mg/kg, respectively. These values were significantly lower than the 0.17 mg/kg and 0.64 mg/kg measured at the Guiyang planting site. This phenomenon is associated with the higher expression levels of the betaine aldehyde dehydrogenase (OsBadh2) gene, enhanced enzyme activities, and a greater content of γ-aminobutyric acid (GABA) in the leaves of Dalixiang at the Meitan planting site. In contrast, the expression levels of genes related to triose phosphate isomerase (OsTPI), proline dehydrogenase (OsProDH), ornithine aminotransferase (OsOAT), and Delta1-pyrroline-5-carboxylic acid synthetase (OsP5CS), along with their corresponding enzyme activities, as well as the contents of methylglyoxal, proline, and ornithine, were lower. In conclusion, due to the influence of the Guiyang environment, the biosynthesis of Dalixiang 2AP was promoted, which made the Dalixiang planted in Guiyang stronger than that planted in Meitan. This study provides a theoretical basis for the selection of the best planting area of Dalixiang and the improvement of Dalixiang flavor through agronomic cultivation techniques.

Heading date (HD) is a critical traits of rice that significantly affects yield and quality. Although researchers identified major-effect genes that involving in HD, they often have dramatic effects on HD and other vital agronomic traits, making them not easy to be applied in molecular breeding practices. To address this constraint, we focused on identifying genes with minor effects on HD that allow fine-tuning flowering time without significant yield loss. Previously, a 150-recombinant inbred lines (RILs) population was constructed from the early-heading date variety V20B and the lateheading variety CPSLO17, and the line RIL-111 showed the intermediate phenotype of heading date between V20B and CPSLO17. In our work, we applied bulked segregant analysis (BSA) with whole genome re-sequencing (WGS) to map quantitative trait locus (QTL) for heading date. In the results, a minor effect QTL, designated as qDTHR, was identified within the 647.1 kb on chromosome 1 of the F₂ population, constructed from RIL-111 and V20B, associating with 14 non-synonymous mutant genes in the interval. The results provide a basis for molecular breeding to improve rice varieties, and lay a foundation for further cloning and functional analysis.

Fat is the third largest substance in rice seeds, and its content has a great impact on rice cooking, taste and storage qualities. However, few genes related to seed fat content have been cloned, which seriously restricts the application of fat traits in high-quality rice breeding. ‘Goudang 3’ is a representative aromatic rice landrace of Guizhou He, a characteristic rice species resource in Guizhou Province, China. It has the advantages of high fat content, rich flavor, soft and glutinous taste, etc. In this work, to address this issue, from a high-fat content rice variety, Goudang 3, and a low-fat content rice variety, Huazhan, a 148 recombinant inbred lines (RILs) population were derived. A high-density genetic map with 4063 Bin Markers covering 12 chromosomes were constructed through simplified genotyping-by-sequencing (GBS) technology. In combination with fat content, a brown rice fat content quantitative trait loci (QTL) qCFC3 was mapped within the 492 kb interval on chromosome 3. The qCFC3 was consistent with the previous reporting site, and no cloned fat content-related genes have been reported. LOC_Os03g13630 was identified. In conclusion, these QTL and candidate gene can be used for improving rice quality and can lay a foundation for further cloning and functional analysis.

Rice is an important staple crop, and fertilization has a very important role in the production of high-yield and well-quality hybrid of rice. The abnormal development of female gametes will lead to a significant decrease in rice yields. Due to the complex mechanism of female gamete development, the molecular mechanism of female sterility has not made a breakthrough. In this study, one semi-sterile mutant m21 and its fifth generation of backcross material (WZN58 and WZN68) were used as materials, and the phenotypic observation and cytological observation of embryo sac development were performed. Moreover, the pollen viability was evaluated by iodine potassium iodide (I₂-KI) staining. Bulked-segregant analysis (BSA) re-sequencing and transgenic analysis were further applied to investigate the molecular mechanism of semi-sterile phenotype. These results demonstrated that male gamete development was normal, while the abnormality of the mutant was caused by the abnormal development of female gamete. Among 112 candidate genes detected by BSA, one gene Os10g0506000 was identified responsible for the semi-sterile phenotype of m21 mutant. This study provides an ideal material and candidate gene for rice female fertility analysis.

Starch synthesized and stored in amyloplasts serves as the major energy storage molecule in cereal endosperm. To elucidate the molecular mechanisms underlying amyloplast development and starch synthesis, we isolated a series of floury endosperm mutants in rice (Oryza sativa L.). We identified the rice mutant floury shrunken endosperm1 (fse1), which exhibited obvious defects in the development of compound starch grains, decreased starch content, and altered starch physicochemical features. Map-based cloning showed that FSE1 encodes a phospholipase-like protein homologous to phosphatidic acid-preferring phospholipase A1. FSE1 was expressed ubiquitously with abundant levels observed in developing seeds and roots. FSE1 was localized to both the cytosol and intracellular membranes. Lipid profiling indicated that total extra-plastidic lipids and phosphatidic acid were increased in fse1 plants, suggesting that FSE1 may exhibit in vivo phospholipase A1 activity on phosphatidylcholine, phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, and, in particular, phosphatidic acid. Additionally, the total galactolipid content in developing fse1 endosperm was significantly reduced, which may cause abnormal amyloplast development. Our results identify FSE1 as a phospholipase-like protein that controls the synthesis of galactolipids in rice endosperm, and provide a novel connection between lipid metabolism and starch synthesis in rice grains during endosperm development.

The CDS Variance Analysis of OsBADH2 Gene and Aroma Appraisal of 7 Guizhou HE ( Oryza sativa )

The contribution of rice as a protein source is important. Rice seed protein can be divided into four forms, glutelin (57 kDa, 37-39 kDa, 22-23 kDa), prolamine (13 kDa), albumin (16 kDa) and globulin (10 kDa, 26 kDa) on its solubility. Glutelin is the major storage protein of rice and accounted for 80% of total protein found in the rice grain, the mature glutelin comprises an acidic (37-39 kDa) and an basic subunit (22-23 kDa) coming from a common precursor (57 kDa) by post-transcriptional hydrolytic cleavage. Prolamine is the second important. Rice seed proteins localize in two types of protein bodies, PB-I, PB-II. PB-I containing prolamine is indigestible, whereas PB-II being rich in glutelin is digestible. The nutritional value of rice could thus be raised by improving its digestible protein glutelin content. On the other hand, the character of low digestible protein is also an important target of rice breeding. Low protein rice is required for the diet of patients with kidney disease. Three glutelin mutants, W3660, W204, W379, were found by screening 168 rice varieties through SDS-PAGE analysis of the seeds total proteins. The amounts of 37-39 kDa and 22-23 kDa glutelin subunits were much lower and that of 13 kDa prolamine polypeptide was higher in W3660 seeds than in ordinary rice; The amounts of 37-39 kDa and 22-23 kDa glutelin subunits in W204 or W379 seeds were between those in W3660 and ordinary rice. Especially, in W379 seed, there was a large quantity of 57 kDa polypeptide. For characterizing the genetics of the glutelin mutant, the cross population between W3660 and Otorokimochi was constructed. SDS-PAGE analysis of the progeny seed total proteins showed, low glutelin content was always accompanied by high prolamine content; all F1 seeds had low glutelin and high prolamine content; the segregation of low glutelin and normal type in F2 seeds was 3:1; the genotypes of F2 plants were deduced by the analysis of F3 seeds, and among F2 plants the ratio of homozygotes of low glutelin, heterozygotes of low glutelin and homozygotes of normal type was about 1:2:1. These results proved that the trait of low glutelin and high prolamine was controlled by a single dominant gene and could be inherited by its progeny.