Starch Properties of Roasting Rice from Naturally High-Resistant Starch Rice Varieties.

This study investigates the effects of moisture content control on the characteristics, properties, and in vitro starch digestion of roasted rice powder made from natural high-resistant starch (RS) rice varieties. The results demonstrate that adjusting the moisture content before roasting significantly affects the RS content of the roasted rice powder. Among various moisture levels tested, the addition of 15% water (rice-to-water ratio of 85:15) before roasting resulted in the highest RS content, reaching 22.61%. Several key parameters of the rice samples before and after optimal moisture control were analyzed, including thermal stability, chain length distribution, volatile flavor composition, and scanning electron microscopy. Additionally, in vitro digestion properties were measured. The findings revealed that the volatile flavor compounds in the high-RS roasted rice significantly increased compared to non-roasted rice. Moreover, the thermal stability of the rice samples improved, and the chain length distribution exhibited significant changes. The water absorption and expansion properties were significantly lower in the high-RS roasted rice. Furthermore, the in vitro starch digestion of the roasted flour made from high-RS rice showed a significantly lower digestion rate compared to common rice, indicating a lower starch hydrolysis index in high-RS rice with the sbe-rs genotype. Overall, the roasting process of natural high-RS rice modifies its characteristics, increases the RS content, enhances the flavor, and results in a lower starch digestion rate compared to common rice. This study provides valuable data for the food industry to promote the application of high-RS rice varieties with mutations in the SBEIIb gene, such as Youtangdao2 (YTD2).

Breeding for three-line japonica hybrid rice combinations with high resistant starch content using molecular marker-assisted selection.

Resistant starch (RS) is beneficial for human health, and especially for diabetics. Considering the high cost and low productivity of the Jiangtangdao 1 rice variety with high RS content, breeding high RS rice varieties exhibiting high productivity is essential. A molecular marker-assisted selection strategy was applied to increase RS content in a three-line hybrid rice variety. The functional rice variety Jiangtangdao 1, which contains sbe3-rs (on chr2) that controls the RS content, was used as the high RS content donor parent. Subsequently, male sterile maintainer and restorer lines containing homozygous sbe3-rs were bred using molecular marker-assisted selection combined with traditional breeding methods. The male sterile line was crossed with the restorer lines to identify the optimal hybrid combination with a high RS content. We obtained four combinations for which the yields were >50% higher than those of the control Jiangtangdao 1. In addition, there was no significant difference in the RS content between the combinations and Jiangtangdao 1. The hybrid rice plants with high RS content exhibited favorable agronomic traits and therefore have broad prospects for commercial application.

Engineering Herbicide-Tolerance Rice Expressing an Acetohydroxyacid Synthase with a Single Amino Acid Deletion.

The acetohydroxyacid synthase (AHAS) is an essential enzyme involved in branched amino acids. Several herbicides wither weeds via inhibiting AHAS activity, and the AHAS mutants show tolerance to these herbicides. However, most AHAS mutations are residue substitutions but not residue deletion. Here, residue deletion was used to engineering the AHAS gene and herbicide-tolerant rice. Molecular docking analysis predicted that the W548 of the AHAS was a residue deletion to generate herbicide tolerance. The AHAS-ΔW548 protein was generated in vitro to remove the W548 residue. Interestingly, the deletion led to the tetramer dissociation of the AHAS, while this dissociation did not reduce the activity of the AHAS. Moreover, the W548 deletion contributed to multi-family herbicides tolerance. Specially, it conferred more tolerance to sulfometuron-methyl and bispyribac-sodium than the W548L substitution. Further analysis revealed that AHAS-ΔW548 had the best performance on the sulfometuron-methyl tolerance compared to the wild-type control. Over-expression of the AHAS-ΔW548 gene into rice led to the tolerance of multiple herbicides in the transgenic line. The T-DNA insertion and the herbicide treatment did not affect the agronomic traits and yields, while more branched-chain amino acids were detected in transgenic rice seeds. Residue deletion of W548 in the AHAS could be a useful strategy for engineering herbicide tolerant rice. The increase of branched-chain amino acids might improve the umami tastes of the rice.

Characterization of an acetohydroxy acid synthase mutant conferring tolerance to imidazolinone herbicides in rice (Oryza sativa).

MAIN CONCLUSION: The acetohydroxy acid synthase S627N mutation confers herbicide tolerance in rice, and the rice variety containing this mutation produces good yields. This variety is commercially viable at Shanghai and Jiangsu regions in China. Weedy rice is a type of rice that produces lower yields and poorer quality grains than cultivated rice. It plagues commercial rice fields in many countries. One strategy to control its proliferation is to develop rice varieties that are tolerant to specific herbicides. Acetohydroxy acid synthase (AHAS) mutations have been found to confer herbicide tolerance to rice. Here, we identified a single mutation (S627N) in AHAS from an indica rice variety that conferred tolerance against imidazolinone herbicides, including imazethapyr and imazamox. A japonica rice variety (JD164) was developed to obtain herbicide tolerance by introducing the mutated indica ahas gene. Imidazolinone application was sufficient to efficiently control weedy rice in the JD164 field. Although the imazethapyr treatment caused dwarfing in the JD164 plants, it did not significantly reduce yields. To determine whether the decrease of the ahas mRNA expression caused the dwarfism of JD164 after imazethapyr application, we detected the ahas mRNA level in plants. The abundance of the ahas mRNA in JD164 increased after imidazolinone application, thus excluding the mRNA expression level as a possible cause of dwarfism. Activity assays showed that the mutated AHAS was tolerant to imidazolinone but the catalytic efficiency of the mutated AHAS decreased in its presence. Moreover, the activity of the mutated AHAS decreased more in the presence of imazethapyr than in the presence of imazamox. We observed no difference in the AHAS secondary structures, but homology modeling suggested that the S627N mutation enabled the substrate to access the active site channel in AHAS, resulting in imidazolinone tolerance. Our work combined herbicides with a rice variety to control weedy rice and showed the mechanism of herbicide tolerance in this rice variety.