Conventional plant breeding, enables integration of desired combination of traits through hybridization and selection. However, adverse effect of linkage drag would require several breeding cycles to eliminate the undesirable traits and to stabilize and accomplish a variety or hybrid. In order to speed up the process and enhance precision and efficiency, new breeding tools are needed. Several New Breeding Techniques (NBTs) have already been developed, including genome editing (GE) technology.

Genome editing tools such as mega nuclease, zinc finger nuclease (ZFNs), Transcription Activator Like Effector Nucleases (TALENs), Clustered Regularly Interspersed Short Palindromic Repeats (CRISPR)- CRISPR associated (Cas) protein, enables targeted mutations by making DNA double strand break2, followed by error prone repair mechanism which permit precise alteration of the targeted nucleotide(s) in DNA. The introduced changes could range from alteration of a single base to deletion/replacement/ structural reorganization of a large genomic region3.

Application of genome editing in the development of elite germplasm, with high yield, quality, and resistance against biotic and abiotic stresses appears promising. Thermo-sensitive genic male sterile (TGMS) lines were developed by editing of a temperature-sensitivity gene (TMS5) by CRISPR/Cas9. Two TGMS mutants, tms5–1 and tms5–2 were generated in the indica rice cultivar Zhongjiazao17 (cv. YK17) background. These mutants are completely sterile at temperatures 24 and 26 °C. F1 hybrids derived from crosses between YK17S (tms5–1) and three different restorer lines outperformed both parental lines with respect to grain yield and related traits1. Rice tolerance to salinity was developed by engineering a Cas9-OsRR22-gRNA expressing vector, targeting the OsRR22 gene in rice. Homozygous mutant lines were examined for their salinity tolerance and agronomic traits. Results showed that, at seedling stage, salinity tolerance of homozygous mutant lines was significantly enhanced compared to wild-type plants. Furthermore, no significant differences for agronomic traits were evident between T2 homozygous mutant lines and wild-type plants4.

Precise, efficient, and rapid genome editing techniques revolutionizing crop improvement by avoiding genetic modification, gene disruption, and introduction of unwanted genes. Genome editing can provide unprecedented solutions to food insecurity and malnutrition by developing higher-yielding, more nutritious crops resilient to the impacts of biotic stresses and climate change.

REFERENCES:

 1BARMAN, H.N., SHENG, Z., FIAZ, S., ZHONG, M., WU, Y., CAI, Y., WANG, W., JIAO, G., TANG, S., WEI, X. and HU, P., 2020. Generation of a new thermo-sensitive genic male sterile rice line by targeted mutagenesis of TMS5 gene through CRISPR/Cas system. BMC Plant Biol., 19(1): 1-9. .

2MOHANTA, T.K., BASHIR, T., HASHEM, A., ABD_ALLAH, E.F. AND BAE, H., 2017. Genome editing tools in plants. Genes, 8 (12): 399.

3PODEVIN, N., DAVIES, H.V., HARTUNG, F., NOGUÉ, F. AND CASACUBERTA, J.M., 2013. Site-directed nucleases: a paradigm shift in predictable, knowledge-based plant breeding. Trends in biotechnology, 31 (6): 375-383. 4ZHANG, A., LIU, Y., WANG, F., LI, T., CHEN, Z., KONG, D., BI, J., ZHANG, F., LUO, X., WANG, J., TANG, J., YU, X., LIU, G., & LUO, L. (2019). Enhanced rice salinity tolerance via CRISPR/Cas9-targeted mutagenesis of the OsRR22 gene. Mol breed, 39: 47.