Progress in Rice Breeding Based on Genomic Research.

The role of rice genomics in breeding progress is becoming increasingly important. Deeper research into the rice genome will contribute to the identification and utilization of outstanding functional genes, enriching the diversity and genetic basis of breeding materials and meeting the diverse demands for various improvements. Here, we review the significant contributions of rice genomics research to breeding progress over the last 25 years, discussing the profound impact of genomics on rice genome sequencing, functional gene exploration, and novel breeding methods, and we provide valuable insights for future research and breeding practices.

Investigation of flavonoid components and their associated antioxidant capacity in different pigmented rice varieties.

Black and red rice are flavonoid-rich and nutritious. However, comprehensive information of flavonoid components in different pigmented rice varieties remain unclear. Here, we analyze the differences in flavonoid components in black, red, and white rice by ultra-high-performance liquid chromatography (UPLC) and metabolome analysis. Cyanidin-3-glucoside (Cy-3-G), peonidin-3-glucoside (Pe-3-G), quercetin, dihydromyricetin, naringin, and taxifolin contents were significantly high in black rice. By contrast, catechin and epicatechin contents were substantial in red rice. Cy-3-G was the main anthocyanin and its content was more than four times that of Pe-3-G in black rice varieties. Trifolin hardly showed specificity and exhibited a high content in all rice varieties. The antioxidant capacity of the red and black rice varieties was significantly higher than that of white rice. Moreover, in black and red rice, quercetin and catechin respectively exhibited the strongest antioxidant capacity and a good contribution toward the total flavonoid content, and mean time, white rice possessed antioxidant capacity main derived from quercetin and trifolin. Besides, the study also found that there was slightly inconsistent results between UPLC and metabolome, because certain components with trace by metabolome were not detected by UPLC, but their combination could play a complementary role in the exploration of metabolic components to confirm the ingredients.

OsINV3 and Its Homolog, OsINV2, Control Grain Size in Rice.

Vacuolar invertase is involved in sugar metabolism and plays a crucial role in plant growth and development, thus regulating seed size. However, information linking vacuolar invertase and seed size in rice is limited. Here we characterized a small grain mutant sg2 (grain size on chromosome 2) that showed a reduced in grain size and 1000-grain weight compared to the wild type. Map-based cloning and genetic complementation showed that OsINV3 is responsible for the observed phenotype. Loss-of-function of OsINV3 resulted in grains of smaller size when compared to the wild type, while overexpression showed increased grain size. We also obtained a T-DNA insertion mutant of OsINV2, which is a homolog of OsINV3 and generated double knockout (KO) mutants of OsINV2 and OsINV3 using CRISPR/Cas9. Genetic data showed that OsINV2, that has no effect on grain size by itself, reduces grain length and width in the absence of OsINV3. Altered sugar content with increased sucrose and decreased hexose levels, as well as changes vacuolar invertase activities and starch constitution in INV3KO, INV2KO, INV3KOINV2KO mutants indicate that OsINV2 and OsINV3 affect sucrose metabolism in sink organs. In summary, we identified OsINV3 as a positive regulator of grain size in rice, and while OsINV2 has no function on grain size by itself. In the absence of OsINV3, it is possible to detect a role of OsINV2 in the regulation of grain size. Both OsINV3 and OsINV2 are involved in sucrose metabolism, and thus regulate grain size. Our findings increase our understanding of the role of OsINV3 and its homolog, OsINV2, in grain size development and also suggest a potential strategy to improve grain yield in rice.