As recent advances in gene editing technologies have enabled rapid and accurate modification of target genes, new varieties are being developed through the application of gene editing technologies in various crop species. In particular, the CRISPR/Cas9 system has become a tool of choice for gene editing because it is much more economical and efficient than previous tools such as ZFN and TALEN, and is being actively used to improve various breeding traits, including biotic and abiotic stress tolerance to overcome the limitations of conventional plant breeding technologies. In this review, we retrieved 210 papers describing the utilization of CRISPR/Cas9 in rice published between 2013 and 2021 and classified them according to the field of study and traits of interest. Further case studies were conducted on 21 and 12 research papers that reported the enhancement of biotic and abiotic stress tolerance, respectively. This demonstrated that CRISPR/Cas9-based gene editing can be highly effective in improving resistance to bacterial (bacterial leaf blight and bacterial leaf streak), fungal (blast, sheath blight), and viral (rice tungro spherical virus, rice black streak virus) diseases as well as various abiotic stresses, including drought, salinity, cold, and heat, in many cases, without diminishing important agronomic traits. As recent technological advances have begun to overcome the major limitations of CRISPR/Cas9 gene editing, such as low HDR efficiency and off-target effects, it is expected that more research on gene function and cultivar development will adopt CRISPR/Cas9 as a major gene editing tool in the future. To effectively apply such innovative technologies in crop improvement, much effort is required to establish more reasonable and detailed policies for regulating crops developed through new breeding technologies.

Plants grown under stress conditions generate excessive reactive oxygen species resulting in cell death. Therefore, plants activate the protection mechanism via antioxidant accumulation. Anthocyanins are flavonoid-derived secondary metabolites with high antioxidant properties. In this study, we analyzed and characterized the promoter region of RsMYB1, a positive regulator of anthocyanin biosynthesis. The RsMYB1 promoter was designed with four different fragment lengths (MP1, -1034; MP2, -830; MP3, -633; and MP4, -430 bp), and then each RsMYB1 promoter region was fused into a GUS gene for Arabidopsis transformation. The expression patterns of the RsMYB1 promoter constructs were analyzed at different developmental stages and under various abiotic stresses. The GUS expression pattern steadily increased with plant growth, and coincided with enzyme activity and a histochemical GUS assay. In response to drought, salt, sucrose, and low temperature, the GUS transcript level was highly expressed in MP4 in parallel with GUS enzyme activity. These assays indicated that the proximal region (-430 to -1 bp) of RsMYB1 was the core sequence that was induced by salt and low temperature. The expression level of RsMYB1 in the leaves of radish was highly activated and was consistent with the anthocyanin content under salt and low temperature conditions. These results suggest that induction of the RsMYB1 gene can activate the biosynthesis of anthocyanins, which are expected to help plants adapt to stress conditions due to their antioxidant activity.

Hypoxia caused by water seeding of rice inhibits germination and often leads to serious problems in seedling establishment and early growth. To solve this problem, it is necessary to develop rice cultivars that can stably germinate and grow under anaerobic environments. In this study, we performed QTL analysis on anaerobic germination (AG) tolerance using 139 recombinant inbred lines (RILs) derived from a cross between Milyang23 and Gihobyeo, and identified two QTLs (qAG2.1, qAG2.2) on chromosome 2. The LOD scores at qAG2.1 and qAG2.2 were 3.30 and 5.31, respectively. The phenotypic variances explained by the QTLs were 9.19% and 14.99%, respectively. The japonica cultivar Gihobyeo provided alleles for AG tolerance at both QTLs. While the chromosomal location of qAG2.2 overlapped with previously identified QTLs for AG tolerance, qAG2.1 was detected in a locus that has not been reported previously. The RILs carrying favorable type alleles for the AG tolerance at both QTLs (qAG2.1 + qAG2.2) expressed 41.0% survival rate under the AG condition, which was significantly higher than those of the RILs carrying single QTL, qAG2.1 (22.0%) or qAG2.2 (26.2%). As the favorable alleles for the two QTLs found in this study derived from the japonica cultivar Gihobyeo, it is expected that they would accompany less linkage drag such as shattering and lodging compared to those derived from indica or landraces. The result of this study would provide useful information for improving AG tolerance of japonica rice cultivars that can be used for water seeding cultivation.

Crops are exposed to various environmental stresses. These have been affecting the growth of crops, resulting in the severe loss of agronomic production in many countries. Therefore, development of new varieties of resistant crops is required to assure the desired productivity of crops in stress conditions. In this study, a putatively stress-related gene BrTSR53 was isolated from Brassica rapa. The BrTSR53 is 481 bp long and contains ORF region of 234 bp. This ORF showed strong sequence similarities to the uncharacterized genes from Arabidopsis. The expression of BrTSR53 was determined by quantitative real-time PCR analysis. After 3 hr, the highest quantities of mRNA were revealed in cold and salt stress treatments. In drought stress treatments, there was the highest expression after 36 hr. Therefore, it was confirmed that the ORF in BrTSR53 should be a gene that confer increased resistance to B. rapa growing in different stress conditions. The ORF region of BrTSR53 gene was cloned into an expression vector, pYES-DEST52, and a new protein with molecular weight of 13 kDa was detected by western blot analysis. Also, stress tolerance tests showed that BrTSR53-ORF transgenic yeast exhibited increased resistance to the salt stresses compared with the control. In conclusion, the present data predicts that novel ORF in BrTSR53 can serve as an important genetic resource for abiotic stress resistance.