Deep beneath the soil surface, an invisible chemical conversation decides whether a crop thrives or is strangled by one of agriculture’s most destructive parasites. At the heart of that conversation are strigolactones, a family of plant hormones derived from carotenoids that serve a double life: inside the plant they regulate architecture and development, while outside the roots they act as recruitment signals for beneficial arbuscular mycorrhizal fungi. Unfortunately, the same molecules are eavesdropped upon by the seeds of parasitic weeds such as Striga, or witchweed, and broomrape, which use them as a germination cue before launching their attack. A recent commentary published in the journal Crop Health by Zeming Huang and Fan Qi, of Zhejiang University, Xianghu Laboratory and The Sainsbury Laboratory, synthesizes a wave of new research showing that the export machinery for these hormones, rather than their production, may be the most promising target for engineering parasite-resistant crops without breaking the ancient symbiosis plants depend upon.
To appreciate why transporters have become the focus, it helps to trace the biosynthetic pathway itself. Strigolactone synthesis begins with the stereoselective isomerization of all-trans-beta-carotene into 9-cis-beta-carotene, a reaction catalyzed by the isomerase DWARF27, or D27. The carotenoid cleavage dioxygenases CCD7 and CCD8 then perform sequential oxidative cleavages that remodel this intermediate into carlactone, the central precursor shared by all strigolactones. From there, cytochrome P450 enzymes of the CYP711A family oxidize carlactone into carlactonoic acid, a pivotal branch-point metabolite. What happens next depends on the plant lineage. In the liverwort Marchantia paleacea, the MAX1 enzyme converts carlactonoic acid into bryosymbiol, whereas in cowpea and tomato, members of the CYP722C subfamily produce the canonical strigolactone orobanchol. A further tomato enzyme, CYP712G1, converts orobanchol into solanacol, the dominant strigolactone in tomato root exudates, while in sorghum the enzyme CYP728B35 transforms 5-deoxystrigol into sorgomol. Legumes appear to deploy yet other enzymes that yield non-canonical compounds such as lotuslactone.
This structural diversity is not accidental; it is the product of hundreds of millions of years of co-evolution with mycorrhizal fungi. In Marchantia paleacea, a bryophyte that diverged early from the lineage leading to vascular plants, secreted strigolactones act both as internal developmental regulators and as rhizospheric signals that induce arbuscular mycorrhizal colonization. Recent work from Wang’s group demonstrated that M. paleacea ccd8a/8b mutants, which cannot synthesize strigolactones, show significantly impaired fungal colonization, an impairment that can be partially rescued by applying the synthetic strigolactone analog GR24 or by root exudates collected from phosphorus-starved plants rich in endogenous strigolactones. The lesson is clear: the hormonal and symbiotic roles of these molecules were intertwined from the very origin of land plant interactions with fungi, long before parasitic weeds entered the picture.
As vascular plants diversified, so did their strigolactone profiles, and with them came an evolutionary trade-off. Monocots such as sorghum predominantly secrete the non-hydroxylated 5-deoxystrigol, a molecule that optimizes mycorrhizal symbiosis under low-phosphorus conditions but inadvertently makes the plant exquisitely vulnerable to Striga, whose germination receptors are tuned to detect it. In contrast, members of the Fabaceae, the legume family, preferentially synthesize hydroxylated strigolactones such as orobanchol and lotuslactone. This specialized chemical profile diminishes recognition by Striga while still maintaining effective mycorrhizal partnerships, representing an evolutionary adaptation that balances symbiotic benefit against parasitic risk. Huang and Qi highlight this contrast as a natural blueprint for crop engineering, and they pose two critical questions for the field: whether hydroxylation modifications determine preferential recognition by mycorrhizal fungi versus parasitic plants, and how transporter-targeted crop systems could be engineered to spatially restrict strigolactone secretion, for example through root tip-specific expression, to suppress Striga germination while preserving symbiosis in nutrient-deprived zones.
The answer to the second question is rapidly taking shape through the study of ABC transporters. In 2012, researchers identified the petunia ABCG gene PLEIOTROPIC DRUG RESISTANCE 1, or PDR1, as the first strigolactone transporter, establishing that these hormones are actively exported rather than passively leaking into the soil. Since then, homologous transporters have been characterized in Medicago truncatula, sorghum and tomato, progressively revealing a conserved export system that plants use to deliver strigolactones into the rhizosphere. It is precisely this system that parasitic weeds exploit, and precisely this system that two landmark studies published in 2025 have now shown can be safely disabled.
The first breakthrough came from Shi and colleagues, who identified two ABCG transporter genes in sorghum, named SbSLT1 and SbSLT2, responsible for exporting strigolactones from roots into the surrounding soil. Transcriptomic and functional analyses confirmed that both transporters are induced under low-phosphorus conditions or by GR24 treatment. Using the protein-structure prediction tool AlphaFold2, the researchers modeled the structures of SbSLT1 and SbSLT2 and validated specific phenylalanine residues, F693 in SbSLT1 and F642 in SbSLT2, as key binding sites for strigolactone molecules. When the team used CRISPR/Cas9 gene editing to knock out these transporters, strigolactone efflux into the rhizosphere collapsed, and Striga seed germination and parasitism were suppressed by 67 to 94 percent, enough to stabilize crop yield under infestation.
Crucially, the sorghum transporter knockouts carried no obvious penalty. In field trials conducted under Striga-free conditions, single knockouts of either SbSLT1 or SbSLT2 and the double knockout showed no growth defects compared with wild-type plants, indicating that the internal hormonal functions of strigolactones, which govern shoot branching and development, remained intact even though export was abolished. In Striga-infested fields, the mutants hosted fewer parasitic plants and suffered significantly lower yield losses than the wild type. Remarkably, the mutants actually accumulated greater aboveground biomass, both fresh and dry weight, than wild-type plants, an effect the authors attribute to prolonged leaf greenness and increased tillering. The result suggests that blocking strigolactone export can convert a devastating yield liability into a modest agronomic advantage, all while leaving the plant’s internal signaling untouched.
A parallel study by Ban and colleagues extended the strategy to tomato, a crop plagued by broomrape rather than witchweed. The team identified two ABCG transporter genes in tomato, SlABCG44 and SlABCG45, which mediate the exudation of orobanchol and solanacol into the soil as well as the upward translocation of these hormones within the plant. Both pot experiments and field trials consistently demonstrated that single knockout mutants of either gene suffered a significant reduction in parasitic infestation by Egyptian broomrape. Even more striking, the yields of two independent Slabcg45 knockout mutants increased by more than 30 percent relative to controls, underscoring the substantial potential of SlABCG45 as a target for breeding parasitic-resistant tomato varieties. Together with the sorghum work, these findings establish transporter editing as a generalizable platform rather than a species-specific curiosity.
The broader vision articulated by Huang and Qi is to integrate artificial intelligence-predicted, evolutionarily conserved motifs of strigolactone transporters with homology-directed CRISPR editing, allowing the strategy to be extended across major crops while minimizing off-target effects on root microbiome assembly. Because the transporters control secretion rather than synthesis, tissue-specific or spatially restricted manipulation could in principle confine strigolactone release to zones where mycorrhizal recruitment is most valuable, starving parasite seeds of their germination cue without depriving the fungal partners. The evolutionary arms race between parasitic plants and their hosts has already produced one elegant countermeasure in legumes, whose distinctive non-canonical strigolactones maintain high mycorrhizal efficacy while evading parasite germination receptors. Deciphering the molecular logic of biosynthetic diversification and spatiotemporal transport regulation, the authors argue, will not only resolve long-standing questions in plant chemical ecology but also provide a mechanistic framework for engineering rhizosphere communication itself, letting breeders borrow natural evolutionary solutions to optimize symbiotic partnerships while minimizing parasitic vulnerability.
For millions of smallholder farmers across sub-Saharan Africa and the Mediterranean basin, where Striga and broomrape inflict losses measured in billions of dollars annually, the prospect of a single gene edit that suppresses parasitism by up to 94 percent without yield penalties represents a genuine turning point. The strigolactone pathway once looked like an intractable dilemma: silence it entirely and plants lose both their branching control and their fungal allies; leave it alone and the parasites win. The new transporter-based approach dissolves that dilemma by decoupling the hormone’s internal duties from its external signal, offering a route to crops that keep their friends and starve their enemies at the same time.
Subject of Research: Engineering strigolactone transporter signaling to confer resistance to parasitic weeds while maintaining arbuscular mycorrhizal symbiosis in crops
Article Title: Engineering strigolactone signaling: toward crops that resist parasites without sacrificing symbiosis
Article References: Engineering strigolactone signaling: toward crops that resist parasites without sacrificing symbiosis. (n.d.). https://doi.org/10.1007/s44297-025-00053-4
Image Credits: AI Generated
DOI: 10.1007/s44297-025-00053-4
Keywords: strigolactones, Striga, broomrape, parasitic weeds, arbuscular mycorrhizal symbiosis, ABC transporters, CRISPR gene editing, sorghum, tomato, plant hormones, rhizosphere signaling, crop breeding
Cite Scienmag News
APA
MLA
Chicago
Juliet Wilcox. (October 2, 2026). Crippling a Hormone Export Route Gives Crops Immunity to Witchweed. Scienmag. https://scienmag.com/crippling-a-hormone-export-route-gives-crops-immunity-to-witchweed/
Juliet Wilcox. “Crippling a Hormone Export Route Gives Crops Immunity to Witchweed.” Scienmag, 2 October 2026, https://scienmag.com/crippling-a-hormone-export-route-gives-crops-immunity-to-witchweed/. Accessed 2 October 2026.
Juliet Wilcox. “Crippling a Hormone Export Route Gives Crops Immunity to Witchweed.” Scienmag. October 2, 2026. https://scienmag.com/crippling-a-hormone-export-route-gives-crops-immunity-to-witchweed/
Copy citation
Download RIS
Tags: ABC transportersarbuscular mycorrhizal fungi symbiosisarbuscular mycorrhizal symbiosisbroomrapecarotenoid-derived plant hormonesCRISPR gene editingcrop breedingcrop parasite resistancegenetic engineering for crop resilienceparasitic weed control strategiesparasitic weedsplant hormone export inhibitionplant hormone transport mechanismsplant hormonesrhizosphere signalingsoil chemical communicationsorghumStrigastrigolactone signaling pathwaystrigolactonessustainable agriculture and parasitic weed managementtargeted disruption of hormone exporttomatowitchweed germination cues
