The core idea behind multiplex genome editing is deceptively simple. Where early genome editing tools such as zinc finger nucleases and transcription activator-like effector nucleases, known as ZFNs and TALENs, required a new engineered protein for every DNA target, CRISPR-based systems use small guide RNAs that can be reprogrammed cheaply and quickly. Multiplexing takes this a step further by deploying two or more guide RNAs simultaneously, allowing researchers to edit multiple loci in a single experiment, sometimes down to the single-nucleotide level. Because of this superior precision and feasibility, the authors note, CRISPR-MGE has largely displaced TALENs and ZFNs in plant laboratories worldwide, becoming the default platform for both functional genomics and applied crop improvement.

Delivering many guide RNAs at once posed an early engineering challenge, and the review catalogs the creative solutions that emerged. The most straightforward approach uses individual expression cassettes, with each guide RNA driven by its own promoter, an effective but bulky strategy that becomes unwieldy as target numbers grow. More elegant systems exploit the cell’s own machinery. The endogenous tRNA-processing system, for example, allows researchers to string multiple guide sequences together in a single synthetic gene, flanked by tRNA sequences that the plant itself cleaves apart to release mature guides. This strategy has been demonstrated in maize, rice, and cabbage, among other species. Alternative approaches borrow from bacterial immunity and RNA biology: the CRISPR-associated endoribonuclease Csy4 can process a polycistronic transcript into individual guide RNAs, while self-cleaving ribozymes, first characterized as simple RNA enzymes in the late 1980s, can be placed around guide sequences to achieve the same result.

Beyond these foundational strategies, the review highlights newer advances that have refined multiplex editing into what the authors describe as a powerful, efficient, and robust toolkit. The Cas12a enzyme, formerly known as Cpf1, has proven especially valuable because it processes its own CRISPR RNA arrays, naturally lending itself to multiplexing while recognizing a different protospacer-adjacent motif than Cas9 and thereby expanding the range of editable genomic sites. Engineered Cas12a variants with relaxed PAM requirements and temperature tolerance have extended editing into rice, maize, and tomato under conditions where earlier systems faltered. At the same time, ultra-multiplexing platforms now permit the simultaneous targeting of dozens of loci, and orthogonal systems such as CRISPR-Combo allow genome editing and transcriptional activation to proceed in parallel within the same cell, a capability demonstrated in tomato and other species.

Perhaps the most consequential shift described in the review is the move toward transgene-free editing. Conventional CRISPR experiments introduce DNA constructs that integrate into the plant genome, leaving behind foreign sequences that complicate regulation and public acceptance. DNA-free alternatives circumvent this problem entirely. Preassembled Cas9 ribonucleoproteins, complexes of purified protein and guide RNA, can be delivered into plant cells by PEG-mediated transfection of protoplasts, lipofection, particle bombardment, or cationic lipid nanoparticles, producing edits that are inherited while the editing machinery itself is rapidly degraded and never integrated. The review cites successful DNA-free editing in potato, maize, canola, soybean, citrus, carrot, and tomato, including the generation of transgene-free canker-resistant sweet orange using Cas12a ribonucleoproteins. Virus-based guide RNA delivery systems offer another route, with vectors derived from potato virus X and other plant viruses shuttling guide RNAs through the plant to generate heritable edits without stable transgene integration.

Why does multiplexing matter so much for stress biology? The answer lies in the architecture of plant stress responses. Transcription factors, the DNA-binding proteins that switch suites of target genes on or off, sit at the hubs of regulatory networks that coordinate a plant’s reaction to abiotic stresses such as drought, salinity, cold, and heat, as well as biotic attacks by pathogens and pests. These networks are notoriously redundant and interconnected: single-gene knockouts often produce subtle or no phenotypes because paralogs and parallel pathways compensate. Multiplex editing cuts through this redundancy by disabling entire gene families or combinations of regulators at once, revealing the true structure of the network. The review emphasizes that this capacity makes CRISPR-MGE ideal for elucidating the function of transcription factors, the key molecular players regulating diverse plant responses, especially within stress pathways.

The empirical record assembled in the review illustrates the point across crops and stress types. In rice, knockout of the OsbHLH024 transcription factor improved salt stress resistance, while editing of NAC-family members such as OsNAC15 and OsNAC45 has illuminated their roles in drought, salt, and abscisic acid responses. In tomato, CRISPR-Cas9 mutagenesis of SlNPR1 reduced drought tolerance, confirming its positive regulatory role, while disruption of SlCBF1 diminished chilling tolerance and loss of SlMYC2 compromised methyl jasmonate-induced fruit resistance to the gray mold pathogen Botrytis cinerea. In wheat, simultaneous editing of the three homoeoalleles of TaEDR1 enhanced powdery mildew resistance, a landmark demonstration of why polyploid crops demand multiplex approaches, since useful traits often require hitting all redundant copies at once. Multiplex editing of BnWRKY11 and BnWRKY70 in oilseed rape, and of stress-linked regulators in poplar and grapevine, round out a picture of a technology operating across the plant kingdom.

The toolkit’s reach extends beyond simple knockouts. Multiplex platforms now support base editing, which converts individual DNA letters without cutting both strands, and prime editing, which can install precise sequence changes; both have been deployed in multiplex form in rice, wheat, and maize for agronomically important genes. Nuclease-dead Cas9 fused to activation or repression domains, such as the VP64 activator or the SRAX repressor domain, enables transcriptional regulation of target genes without altering their sequence, and epigenome editing fusions, such as a histone acetyltransferase tethered by dCas9, have improved drought tolerance in Arabidopsis. Metabolic engineering applications, from boosting gamma-aminobutyric acid and lycopene in tomato to raising carotenoid and isoflavone levels in rice and soybean, demonstrate that multiplex editing can reconfigure entire biosynthetic pathways, the same logic needed to tune stress-responsive hormone and antioxidant networks.

The review also confronts the practical bottlenecks that still separate laboratory success from farmers’ fields. Plant regeneration remains a limiting step for many species and genotypes, though morphogenic regulators such as GRF-GIF chimeric proteins and growth-regulating factors are boosting transformation efficiency in crops like sorghum and wheat. Quantifying editing outcomes has grown more rigorous with droplet digital PCR and microfluidic chip-based digital PCR, which allow precise measurement of edit frequencies, an important safeguard given that off-target mutations and variable on-target activity remain persistent concerns. Regulatory landscapes, which differ between process-based and product-based frameworks across jurisdictions, will shape how quickly edited stress-tolerant varieties reach the market, and the authors implicitly position transgene-free methods as a way to ease that transition.

Taken together, the review delivers a clear message to the plant science community: advanced multiplex genome editing is no longer an experimental luxury but the central instrument for decoding and redesigning stress-responsive transcription factor networks. As the authors argue, deploying these tools for the functional characterization of stress-responsive transcription factors holds genuine potential to accelerate crop improvement at a moment when rising salinity, erratic rainfall, and emerging pathogens threaten harvests across South Asia and beyond. The convergence of ultra-multiplexing, orthogonal regulation, DNA-free delivery, and precision base and prime editing means that researchers can now ask, and answer, questions about genetic redundancy and network logic that were unanswerable only a few years ago. The next generation of climate-resilient crops, the review suggests, will be written not one gene at a time, but in whole regulatory paragraphs.

Subject of Research: CRISPR multiplex genome editing of stress-responsive transcription factor networks for crop improvement

Article Title: Advances in CRISPR multiplex gene editing to map and modify stress-responsive transcription factor networks for crop improvement

Article References: Sharma, N. N., Kumari, A., Vashisht, I., & Sharma, M. K. (2026). Advances in CRISPR multiplex gene editing to map and modify stress-responsive transcription factor networks for crop improvement. Plant Cell Reports, 45(9), Article 277. https://doi.org/10.1007/s00299-026-03956-w

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03956-w

Keywords: CRISPR, multiplex genome editing, transcription factors, stress response, crop improvement, Cas12a, base editing, prime editing, transgene-free editing, drought tolerance, salt tolerance, plant biotechnology

The limitations of conventional breeding are stark. Hybridization-based pyramiding of favorable genes typically requires ten to fifteen years per cycle, and screening efficiency is low. Worse, genetic linkage often ties desirable genes to undesirable neighbors on the same chromosome, producing genetic drag that breeders cannot easily escape. Because recombination during crossing is random, traditional methods cannot target multi-gene networks or create rare combinations of favorable alleles that simply do not exist in nature. Crop yield itself is not governed by a single gene but emerges from synergistic interactions among growth, disease resistance, pest resistance and stress tolerance networks, while quality traits involve nutrition, taste and appearance simultaneously. Single-trait improvement, the review concludes, leaves an inherent gap between what breeding can deliver and what modern agriculture needs.

Multiplex genome editing closes that gap by exploiting the core mechanics of the CRISPR/Cas system. A single guide RNA forms a ribonucleoprotein complex with a Cas endonuclease, recognizes target double-stranded DNA through base pairing and a protospacer adjacent motif, and induces a site-specific double-strand break. Cellular repair then proceeds through error-prone non-homologous end joining, whose small insertions and deletions can knock out a gene by frameshifting its reading frame, or through template-directed homology-directed repair. The decisive advantage of MGE is that a single vector, delivered in one transformation, can carry guides for many loci at once, coordinating expression across pathways without touching unrelated genes.

The technology’s power is clearest in cases where single-gene edits fail. Genetic redundancy means that mutating one member of a gene family often produces no visible phenotype because homologous genes compensate. In wheat, broad-spectrum resistance to powdery mildew was achieved only by simultaneously mutating all three homoeoalleles of the TaMLO gene family across the A, B and D genomes; plants with a single copy knocked out remained susceptible. The same principle holds in Arabidopsis, where the AtMLO2/6/12 triple mutant shows markedly enhanced pathogen resistance. The review traces the field’s milestones from early two-guide experiments in Arabidopsis and rice, through the tRNA-sgRNA tandem arrays that let one transcript yield many mature guides, to the current record of thirteen target sites edited simultaneously in rice.

Three co-expression architectures dominate the toolkit. The Multi-Transcriptional Unit system drives each sgRNA with its own RNA polymerase III promoter, offering modular control but risking plasmid recombination from repeated promoter sequences and producing bulky vectors. The Twin-Transcriptional Unit system separates Cas9 and sgRNA expression, processing a single polycistronic precursor with tRNA, Csy4 ribozyme or Hammerhead elements; the tRNA strategy, which hijacks the plant’s own RNase P and RNase Z machinery, achieved over fifty percent simultaneous mutation of three genes in rice and supports a modular toolkit for up to eight targets. The Single Transcriptional Unit system fuses Cas9 and sgRNAs into one compact transcript, ideal for species like soybean that tolerate vector redundancy poorly. Species choice matters: monocots such as rice and wheat favor MCTU and TCTU designs, while dicots often require species-specific Pol II promoters and careful control of tandem target numbers.

Applied outcomes span every major breeding goal. In disease resistance, simultaneous targeting of the Bsr-d1, Pi21 and ERF922 genes produced rice varieties resistant to both blast and bacterial blight, with field durability two to three years longer than single-gene lines, because pathogens must overcome multiple infection barriers at once. In abiotic stress, editing three genes governing root development, grain shape and cold response yielded rice that lost only 3.2 percent of yield under cold stress, compared with fifteen to twenty percent losses in conventional cold-tolerant varieties. Tomato plants edited at the HyPRP1 gene gained over forty percent salt tolerance plus cross-resistance to drought and cold. Yield work has been equally striking: editing GS3, TGW3 and GW8 produced high-yielding hybrid rice with slender grains, while combining eight sgRNAs against cytochrome P450 homologs and the BADH2 gene boosted yield and endowed grains with a fragrant aroma.

Quality improvement may be the most commercially compelling frontier. In soybean, knocking out the GmFAD2-1A and GmFAD2-1B desaturase genes created high-oleic-acid oil with better oxidative stability, and stacking those edits with lipoxygenase knockouts removed the beany flavor that limits soy products. Combining two multiplex-edited soybean varieties allowed researchers to tune protein functionality, including emulsifying activity, gelation and solubility, by editing storage protein genes such as Glycinin and beta-Conglycinin. In tomato, simultaneous editing of the PSY1, MYB12 and SGR1 genes recolored fruit and improved nutrition, while triple knockout of LCY, SGR1 and BLC1 blocked carotenoid branch metabolism and raised lycopene accumulation fivefold. Wheat edited across eight gliadin genes points toward hypoimmunogenic bread, and knocking out three soybean lipoxygenase genes eliminated off-flavors.

Perhaps the most visionary application is de novo domestication. Because centuries of artificial selection narrowed the genetic base of crops and discarded valuable stress-resistance traits found in wild relatives, MGE offers a shortcut: edit domestication genes directly in wild germplasm. Researchers established the first de novo domestication system for wild allotetraploid rice, Oryza alta, editing homologs controlling seed shattering, awn length, plant height and grain traits. Even more dramatic, the salt-tolerant landrace Sea Rice 86 was improved by synchronously editing thirteen key agronomic genes in a single transformation; the resulting homozygous line retained its salt tolerance while gaining improvements in plant height, architecture, grain shape, yield components and photoperiod sensitivity. Wild tomato has likewise been rapidly domesticated with eight sgRNAs targeting six agronomic genes, producing larger fruits and higher lycopene content.

Challenges remain substantial. Gene interactions can be antagonistic as well as synergistic: editing rice grain length, width and number genes together raised yield, but loss of Gn1a overactivated cytokinin signaling, multiplying tillers and undermining lodging resistance, a problem that had to be solved by recombining targets such as Ghd7, DTH8 and OsNAC006. Editing efficiency decays with scale, holding at fifty to seventy percent for three to five genes but dropping below thirty percent beyond eight targets. New tools are responding: Cas12a uses short crRNAs that cut sequence redundancy by more than half, processes its own arrays without exogenous enzymes, and engineered variants like Mb3Cas12a now work across relaxed PAM sites and low temperatures. Prime editing, which installs precise changes without double-strand breaks, achieved 28.6 percent dual-site and 7.1 percent quadruple-site efficiency in rice, while an ultra-efficient tomato system reached 87.5 percent single-target precision with multiplex rates matching single edits.

Delivery and design are the next battlegrounds. Agrobacterium transformation and particle bombardment remain mainstream but struggle with large multiplex vectors and recalcitrant species, and both depend on laborious tissue culture. Virus-induced genome editing offers a way out: a Barley stripe mosaic virus system delivering sgRNAs into Cas-expressing wheat reached up to 47.3 percent dual-gene editing in the first generation, with over eighty percent of mutants virus-free by the next, while SYNV vectors can carry the entire CRISPR/Cas machinery in one round. On the design side, machine learning and large language models such as CRISPR-GPT are automating sgRNA selection, and AlphaFold-guided editing has already produced high-oil soybean alleles by predicting which mutations preserve protein structure. The review’s authors frame the trajectory clearly: as efficiency bottlenecks fall and intelligent design matures, multiplex genome editing is propelling crop breeding from experience-dependent craft toward precision engineering of complex, customized traits, a shift with consequences for global food security that are only beginning to unfold.

Subject of Research: CRISPR/Cas-mediated multiplex genome editing for pyramiding multiple agronomic traits in crop breeding

Article Title: Multiplex gene editing drives revolution in crop breeding: overlaid editing of multiple genes and customization of complex traits

Article References: Multiplex gene editing drives revolution in crop breeding: overlaid editing of multiple genes and customization of complex traits. (n.d.). https://doi.org/10.1007/s44307-026-00099-7

Image Credits: AI Generated

DOI: 10.1007/s44307-026-00099-7

Keywords: CRISPR/Cas9, multiplex genome editing, crop breeding, trait pyramiding, Cas12a, prime editing, de novo domestication, rice, soybean, tomato, wheat, virus-induced genome editing