Plants produce and accumulate stress-resistant substances when exposed to abiotic stress, which involves a protein conversion mechanism that breaks down stress-damaged proteins and supplies usable amino acids. Eukaryotic protein turnover is mostly driven by the ubiquitination pathway. Among the three enzymes required for protein degradation, E3 ubiquitin ligase plays a pivotal role in most cells, as it determines the specificity of ubiquitination and selects target proteins for degradation. In this study, to investigate the function of OsPUB7 (Plant U-box gene in Oryza sativa), we constructed a CRISPR/Cas9 vector, generated OsPUB7 gene-edited individuals, and evaluated resistance to abiotic stress using gene-edited lines. A stress-tolerant phenotype was observed as a result of drought and salinity stress treatment in the T₂ OsPUB7 gene-edited null lines (PUB7-GE) lacking the T-DNA. In addition, although PUB7-GE did not show any significant change in mRNA expression analysis, it showed lower ion leakage and higher proline content than the wild type (WT). Protein–protein interaction analysis revealed that the expression of the genes (OsPUB23, OsPUB24, OsPUB66, and OsPUB67) known to be involved in stress increased in PUB7-GE and this, by forming a 1-node network with OsPUB66 and OsPUB7, acted as a negative regulator of drought and salinity stress. This result provides evidence that OsPUB7 will be a useful target for both breeding and future research on drought tolerance/abiotic stress in rice.

Ninety-five percent of the general nutrients in rice are concentrated in the rice bran and germ, and many nutrients such as vitamins, minerals, dietary fiber, and essential fatty acids, as well as antioxidants such as tocopherol, are lost during milling. In this study, we investigated the thickness of seed coat and aleurone layers using a 294 rice core collection, and found candidate genes related to thickness of seed coat and aleurone layers, by performing a genome wide association study (GWAS) analysis using whole genome resequencing data. Two primer pairs that can be used as high-resolution melting (HRM) markers were developed. As a result of genotyping BC₂F₂ individuals derived from a cross between “Samgwang” and “Seolgaeng”, and using corresponding HRM markers, it was possible to finally develop HRM markers for selecting seed coat and aleurone layer thickness. This is expected to be used as basic data for the application of gene editing using CRISPR/Cas9 technology and for establishing a breeding strategy for high eating quality rice using molecular genetic technology.

Brown rice is composed of rice bran, pericarp, seed coat, and aleurone layers, and the rice bran layer contains a large number of substances useful for the human body, such as dietary fiber, α-tocopherol, α-tocotrienol, and vitamins. However, more than 90% of these substances are removed when polished, and white rice has the disadvantage of losing food-related ingredients, such as umami-related amino acids, when compared to the unpolished group. In this study, we tried to develop new breeding lines with a thinner seed coat and aleurone layer to provide high eating quality with softer chewing characteristics and processability in rice grain. We detected an SNP for foreground selection for the backcross population by comparing genome sequences between Samgwang and Seolgaeng and developed high eating quality brown rice breeding lines by applying marker-assisted backcrossing (MAB_C) breeding programs to backcross populations between Samgwang and Seolgaeng using KASP markers. SNP markers for foreground selection were identified to improve eating and processability through SNP mapping of Samgwang and Seolgaeng with SSIIa as a target gene in this study. Line selection according to genotype of KASP markers was successful in BC₁F₁ and BC₂F₁ generations, with the recurrent parent genome recovery ratio ranging from 91.22% to 98.65%. In BC₂F₁ seeds of the selected lines, thickness of the aleurone layer was found to range from 13.82 to 21.67 μm, which is much thinner than the 30.91 μm of the wild type, suggesting that selection by MABc could be used as an additional breeding material for the development of highly processed rice varieties. These lines will be useful to develop new brown rice varieties with softer chewing characteristics and processability in rice grain.