Maize Genomics and Genetics 2025, Vol.16, No.4, 229-238 http://cropscipublisher.com/index.php/mgg 231 ZmALS2 changes from C to T, it shows strong resistance to herbicides like chlorosulfonon. Looking at EPSPS, scientists added three amino acid mutations to natural ZmEPSPS through base editing. As a result, corn not only tolerated glyphosate but also had its yield unaffected. There are also transgenic routes, such as cp4-epsps or gr79-epsps, which are also common methods for glyphosate resistance breeding at present (Yu et al., 2023). For mesotrione, certain haplotypes of CYP81A9 or their high expression status can make corn more resistant to this herbicide (Zhang et al., 2024). As for ZmGHT1, this gene has also begun to attract attention in glufosinate-ammonium resistance, seemingly in connection with a specific one. Figure 1 Representative schematic diagrams of CRISPR/Cas editing. (A) Cas9 applies the PAM and sgRNA to cleave the target DNA and produce a DBS, which is repaired by NHEJ or HDR; (B) Cas12a uses a RuvC domain under the guidance of crRNA without the participation of tracrRNA to cleave dsDNA, producing a sticky end; (C) Cas13a targets RNA in the nucleus; (D) CRISPR/Cas14a targets ssDNA cleavage under the direction of sgRNA, and does not require a PAM sequence, producing SSB; (E) CBE system compliments the single base replacement of the target site C-T (G-A), cleaves a single target locus, and produces a staggering cut; (F) ABE system compliments a single base substitution of A-G (T-C), cleaving at the targeted loci, and displaces the DNA fragment, leaving a staggering end in dsDNA (Provided by BioRender.com; accessed on 14 March 2022) (Adopted from Min et al., 2022) 3.3 Strategies for multiplex base editing to enhance resistance spectrum A single gene mutation might not be sufficient; in such cases, multiple base editing needs to be employed. Some studies have attempted to simultaneously edit ALS and EPSPS, so that corn can develop resistance to several herbicides, no longer relying on a single mechanism of action, and also slow down the rate at which weeds develop resistance (Li et al., 2020). Another strategy is "combined resistance", for instance, by modifying genes such as ALS, EPSPS, CYP81A9 and ZmGHT1 together, or directly introducing multiple genes (such as cp4-epsps, bar, etc.) in a single transgenic event, corn can be resistant to glyphosate, glufosinate-ammonium and sulfonylurea herbicides simultaneously (Li et al., 2023). It is worth noting that nowadays, an increasing number of studies tend to favor methods that do not use exogenous DNA, such as base editing, which is not only precise and hereditary but also easier to regulate and more readily accepted by the public.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==