Two-Layer Gene Editing Delivers Elite Herbicide-Tolerant Crops

For decades, crop scientists have chased a deceptively simple goal: redesigning a plant’s own genes so that it can shrug off the herbicides farmers depend on. Most attempts have edited either the protein a herbicide attacks or the regulatory DNA that controls how much of that protein the plant makes. A new study published in Nature Plants argues that this either-or approach is precisely why so many engineered traits fall short. By editing both layers at once — the coding sequence of a key enzyme and the cis-regulatory elements that govern its expression — researchers have assembled what they call elite herbicide-tolerance alleles in rice and wheat, two of the world’s most important staple crops.

The target of the work was 4-hydroxyphenylpyruvate dioxygenase, or HPPD, an enzyme that sits at a critical junction in plant metabolism. HPPD catalyzes a step in the breakdown of tyrosine that feeds the production of homogentisate, a precursor required for plastoquinone and tocopherol synthesis. Plastoquinone, in turn, is essential for carotenoid biosynthesis, and carotenoids protect the photosynthetic machinery of chloroplasts from oxidative damage. This dependency is exactly what makes HPPD such an effective herbicidal target: compounds that inhibit the enzyme, including widely used triketone herbicides such as mesotrione, starve plants of carotenoids, causing bleaching of newly emerged tissue and ultimately death. Weeds, crops, and everything green in between share this vulnerability, which is why engineering tolerance at the HPPD locus has long been an attractive but difficult proposition.

The difficulty lies in a classic trade-off. Mutations in the coding sequence of HPPD that weaken herbicide binding tend also to compromise the enzyme’s catalytic performance, because the herbicide-binding pocket overlaps with the chemistry the enzyme must perform. A plant carrying such a mutation may survive spraying, but it pays a growth penalty. Conversely, simply cranking up expression of an unmodified HPPD gene can raise the amount of enzyme available and dilute the herbicide’s effect, but regulatory overexpression often brings pleiotropic problems — metabolic imbalance, developmental defects, and unpredictable performance across genetic backgrounds and environments. The research team behind the new study recognized that dosage-sensitive traits like herbicide tolerance demand simultaneous optimization of both protein function and protein abundance.

Their solution was a dual-layer strategy. On the first layer, they used structure-guided protein design to identify amino acid substitutions in HPPD that would reduce sensitivity to herbicide inhibitors while preserving catalytic activity. Rather than screening random mutagenesis libraries, the researchers reasoned from the three-dimensional structure of the enzyme, focusing on positions that line the inhibitor-binding site but sit at a tolerable distance from the catalytic machinery. This rational approach, informed by computational tools for protein engineering that integrate structural and evolutionary constraints — an area that has advanced rapidly with artificial-intelligence-based inverse-folding models — allowed them to prioritize a small set of candidate substitutions with a high probability of decoupling inhibitor binding from enzymatic function.

On the second layer, the team turned to cis-regulatory engineering at the endogenous HPPD locus. Instead of inserting a transgene under a strong constitutive promoter, they edited the native promoter and regulatory regions of the crop’s own HPPD gene to tune its expression upward in the tissues where tolerance matters most. Because the edits were made in cis, at the gene’s natural address in the genome, the resulting plants carry modified versions of their own gene rather than foreign DNA constructs. This endogenous approach matters both scientifically and commercially: it preserves native regulation as much as possible, reduces the risk of position effects and silencing that plague transgenic insertions, and may ease the regulatory and public-acceptance pathways for edited crops in jurisdictions that distinguish gene-edited from transgenic plants.

Neither layer alone was sufficient. Coding-sequence edits that conferred reduced herbicide sensitivity produced plants whose tolerance was real but incomplete, while regulatory edits alone raised enzyme levels without addressing the fundamental vulnerability of the wild-type protein to inhibition. It was the combination — an enzyme variant less easily poisoned, produced at elevated levels from its own tuned promoter — that produced the striking tolerance phenotypes. The authors describe these combined versions as elite alleles: single, precisely defined haplotypes at the native locus that deliver a trait at a level useful for breeding, without the need for transgenes or multi-gene stacks.

Demonstrating the strategy in both rice and wheat is a significant part of the result. Rice, a model grass with a compact genome and efficient editing protocols, served as the development platform, but wheat presents a far harder engineering challenge because of its large polyploid genome, in which multiple homoeologous copies of genes must often be edited in concert to see an effect. That the dual-layer approach transferred between these two species suggests it is not a quirk of one crop’s genetics but a generalizable design principle for engineering dosage-sensitive traits — traits whose performance depends on getting both the quality and the quantity of a gene product right.

The implications extend well beyond herbicide tolerance. Herbicide-resistant weeds are a mounting global problem, documented across hundreds of species and virtually every major herbicide class, and new tolerance traits are needed both to replace overused chemistries and to enable rotation between different modes of action — a practice that slows the evolution of resistance in weed populations. An HPPD-based tolerance allele generated by editing native sequences could be introduced into elite breeding lines by conventional crossing once created in a donor background, or recreated directly in elite germplasm by editing, dramatically shortening the path from discovery to farmers’ fields compared with transgenic trait development.

More broadly, the study offers a template for how genome editing in crops is maturing. Early editing work largely mimicked loss-of-function genetics, knocking out genes to study their roles or eliminate undesirable traits. The frontier is now precision gain-of-function engineering: redesigning proteins in place, tuning their expression from native regulatory landscapes, and combining these edits into coherent alleles that behave predictably. The same dual-layer logic could apply to other dosage-sensitive agricultural targets, including disease resistance genes, nutrient biosynthetic pathways, and tolerance to drought, salinity, or heat, where both the biochemical properties of a protein and the amount of it a tissue produces determine the phenotype.

Challenges remain before elite HPPD alleles reach commercial reality. Edited crops must clear regulatory review in each market, and the agronomic performance of tolerance alleles must be validated across seasons, soils, and herbicide application regimes. Fitness costs of modified enzyme variants, if any, will need to be quantified over full crop lifecycles, and stewardship plans will be required to manage resistance evolution in weed populations exposed to HPPD-inhibiting chemistry. Yet the conceptual advance is clear and consequential: by treating a gene’s coding sequence and its regulatory architecture as a single coordinated design problem, plant biologists have shown that traits once requiring transgenic stacks can be built into the crop’s own genome, one precisely placed edit at a time. For a world that needs higher yields on finite land under intensifying weed pressure, that is a blueprint worth watching closely.

Subject of Research: Dual-layer genome editing of coding and cis-regulatory sequences at the HPPD locus to engineer herbicide-tolerant rice and wheat

Article Title: Coordinated editing of coding and regulatory sequences creates elite herbicide-tolerant alleles

Article References: Coordinated editing of coding and regulatory sequences creates elite herbicide-tolerant alleles. (n.d.). https://doi.org/10.1038/s41477-026-02426-1

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02426-1

Keywords: genome editing, herbicide tolerance, HPPD, rice, wheat, cis-regulatory engineering, protein design, crop breeding, gene editing, plant biotechnology, elite alleles, Nature Plants