CRISPR tomato line promises cheaper hybrid seeds with visual sterility marker

Tomato breeders may soon retire one of the most tedious rituals in their trade. In a study published in BMC Plant Biology, researchers at Northwest A&F University in Yangling, China, report using CRISPR/Cas9 gene editing to create a male-sterile tomato line that carries a built-in visual marker, a green hypocotyl, allowing workers to identify sterile seedlings at a glance rather than relying on laborious manual emasculation. The work, led by Dan Luo, Shufen Wang and Xiaofeng Wang, targets a bottleneck that has long constrained the tomato seed industry: although F1 hybrid tomatoes deliver remarkable uniformity, vigor and stress resistance, producing their seeds still depends overwhelmingly on hand pollination because suitable male-sterile breeding materials remain scarce.

The scientific logic behind the advance rests on two simultaneous gene knockouts. The team disabled Ms10³⁵, a gene essential for male fertility whose loss renders plants unable to produce viable pollen, and F3H, which encodes flavanone 3-hydroxylase, an enzyme in the flavonoid biosynthesis pathway. Knocking out F3H disrupts anthocyanin pigment accumulation in seedlings, producing the distinctive green hypocotyl that serves as a morphological flag for the sterile genotype. The resulting dual-mutant line, designated CR-ms10³⁵/f3h, therefore combines sterility and marker in a single genetic background, a design intended to simplify screening during hybrid seed multiplication.

CRISPR/Cas9 editing works by programming a guide RNA to direct the Cas9 nuclease to precise genomic targets, where it introduces double-strand breaks that the cell repairs imperfectly, often deleting or inserting bases that disable the gene. Because the edits are small and targeted, breeders can segregate away the transgenic editing machinery in subsequent generations. The researchers confirmed this in their crosses: PCR assays detected no trace of Cas9 or NPTII, a selectable marker used during transformation, in the F1 hybrid offspring. That absence matters commercially, since transgene-free hybrids face fewer regulatory hurdles and less consumer resistance in many markets.

To test whether the edited sterile line could actually serve hybrid seed production, the team used CR-ms10³⁵/f3h and the wild-type inbred line 19-1 as maternal parents, crossing each with two paternal lines, 1# and 8#. They then compared the agronomic performance of the resulting F1 hybrids. The verdict was clear: hybrids derived from the gene-edited sterile mothers showed no significant differences from those produced through conventional manual emasculation. Yield-related traits, plant architecture and other measured characteristics were effectively indistinguishable, indicating that the editing strategy leaves hybrid performance undetectably altered.

The significance of that result extends beyond tomatoes. Manual emasculation and pollination are among the most expensive steps in hybrid seed multiplication for self-pollinating crops, and labor costs have been rising across major seed-producing regions. Male sterility offers a genetic shortcut: sterile maternal plants cannot self-fertilize, so every seed they set must result from cross-pollination by the chosen paternal line. The challenge has always been identifying and maintaining the sterile plants within a segregating population, which is precisely where the green hypocotyl marker earns its keep, allowing sterile seedlings to be spotted visually in seedling trays without molecular assays or waiting for flowering.

However, the study also surfaced an important complication. The researchers detected incomplete co-segregation between the green-hypocotyl marker and male sterility, with a recombination rate of approximately five percent. In practical terms, roughly one in twenty seedlings carrying the marker may not be sterile, or vice versa, because the two edited loci sit on different chromosomes and can recombine independently during meiosis. This five percent error rate means visual screening alone cannot guarantee perfect purity, and the authors are candid that more accurate screening methods will be needed before the system reaches industrial reliability.

To address that gap, the team generated a seed-fluorescent transgenic line carrying a functional copy of the Ms10³⁵ gene together with a DsRed2 marker, which makes seeds glow red under appropriate light. This construct is designed as a candidate material for developing an artificial maintainer line, a breeding tool in which a fertility-restoring transgene is introduced into a sterile background so that the maintainer can propagate the sterile line while its own seeds remain visually distinguishable. Such maintainer systems, long pursued in crops like rice and rapeseed, could allow the sterile maternal line to be multiplied without segregation errors, effectively closing the loop on the five percent recombination problem.

The technical details of the maintainer concept deserve unpacking. In a three-line hybrid seed system, a cytoplasmic or nuclear male-sterile line is multiplied by crossing with a maintainer that is genetically identical except for a fertility-restoring gene. Seeds from that cross are all sterile, while seeds from the maintainer’s self-pollination carry the restorer and can be identified by the fluorescent marker. The DsRed2-tagged Ms10³⁵ construct created by the Chinese team is a first step toward engineering such a system in tomato, where the restorer transgene would be tightly linked to a visible seed marker, allowing commercial seed producers to separate sterile maintainer-propagated seeds from restorer seeds mechanically rather than genetically.

What makes the study notable in the broader landscape of crop biotechnology is its pragmatism. Rather than pursuing exotic traits, the researchers applied CRISPR/Cas9 to solve a concrete industrial problem: the scarcity of male-sterile materials for hybrid seed production in a self-pollinating crop. The dual knockout strategy, pairing a sterility gene with a morphological marker, is a template that could be replicated in other vegetable crops where similar bottlenecks exist. The authors suggest the approach could simplify hybrid seed production not only in tomato but potentially in other crops where male sterility and visual markers can be engineered together.

Published as open access with a permanent DOI, the study arrives at a moment when CRISPR-edited crops are moving from laboratory curiosities to commercial realities across several jurisdictions. The transgene-free status of the resulting hybrids, confirmed by PCR, positions the technology favorably under regulatory frameworks that distinguish targeted edits from transgenic modifications. As labor costs continue to climb and demand for high-quality hybrid vegetables grows, tools like the CR-ms10³⁵/f3h line may prove essential for keeping hybrid seed production economically viable, turning what was once a hand-crafted process into something approaching an automated genetic system.

Subject of Research: CRISPR/Cas9-mediated generation of a green hypocotyl-marked male-sterile line for hybrid seed production in Solanum lycopersicum

Article Title: CRISPR/Cas9-mediated generation of a green hypocotyl-marked male-sterile line for hybrid seed production in Solanum lycopersicum

Article References: Luo, D., Jiang, M., Du, J., Liu, J., Huang, S., Deng, R., Zhang, S., Li, Y., Fu, S., Khan, M., Fan, Z., Wang, S., & Wang, X. (2026). CRISPR/Cas9-mediated generation of a green hypocotyl-marked male-sterile line for hybrid seed production in Solanum lycopersicum. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09956-y

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09956-y

Keywords: CRISPR, Cas9-mediated, generation, green, hypocotyl-marked, male-sterile, line, hybrid, seed, production, Solanum, lycopersicum