How a Rare Medicinal Plant Builds Its Silkworm-Like Rings: Multi-Omics Study Reveals the Mechanism

Deep in the mountains of Gansu Province, China, a rare medicinal plant called Notopterygium incisum produces one of the strangest underground structures in the plant kingdom. Its rhizome, the thick horizontal stem that runs beneath the soil, develops a series of constricted segments that resemble the body of a silkworm. In traditional Chinese medicine, rhizomes with these pronounced ring patterns are prized under the name Can Qiang, and dealers have long considered the silkworm-like rings a hallmark of authentic, high-quality material. Yet for all the commercial and cultural weight attached to these rings, no one had ever explained how they actually form. A new study published in BMC Plant Biology by Wenlong Zhao, Jie Gao, Ling Jin and colleagues at Gansu University of Traditional Chinese Medicine now provides the first detailed account, combining anatomy, metabolomics and transcriptomics to trace the rings back to a precise developmental window and a coordinated genetic program.

The team began with classical plant anatomy, sectioning rhizomes at different ages to see exactly when and where the ring pattern emerges. Their analysis revealed that the rings are not laid down gradually throughout the plant’s life. Instead, they arise during a sharply defined critical period, from 126 to 139 days after germination, which falls in early autumn. During this window, the rhizome undergoes uneven secondary growth, the same kind of lateral thickening that widens tree trunks. Crucially, the growth is not uniform around the organ’s circumference. Localized patches of cork cambium, the meristematic tissue that produces protective periderm, become active in some regions while remaining dormant in others. The result is a segmented architecture in which swollen, lignified bands alternate with constricted zones.

The anatomical work also uncovered a second, more dramatic process: programmed cell death in the cortex, the outer tissue layer of the rhizome. As the secondary xylem, the water-conducting wood at the core, expands outward, it exerts mechanical pressure on the surrounding cortex. The cortical cells, already primed for destruction by the plant’s own genetic instructions, are compressed until they collapse, leaving hollow cavities inside the constriction zones. This combination of localized cork cambium activity, xylem-driven compression and cortical cell death produces the multilayered rings and internal voids that give the rhizome its silkworm appearance. In effect, the plant sculpts itself from the inside out, sacrificing its own cortical tissue to create a segmented, hollow-strengthened organ.

To understand what drives this sculpting at the molecular level, the researchers turned to metabolomics, profiling the full complement of small molecules in the developing rhizomes. The analysis revealed a pronounced shift in carbon allocation toward the phenylpropanoid pathway, the metabolic assembly line that plants use to build lignin, the tough polymer that reinforces cell walls. Lignin precursors such as coniferyl alcohol and its storage form coniferin accumulated substantially during the critical period, providing abundant substrate for secondary wall deposition and the lignification of the forming rings. At the same time, the team measured a decrease in core energy metabolites such as succinate, a key intermediate of the citric acid cycle. This pattern points to a metabolic trade-off: the plant is diverting carbon and energy away from general metabolism and toward structural reinforcement, much as a builder diverts materials from interior finishing to fortify a load-bearing wall.

The transcriptomic side of the study identified who is giving the orders. By sequencing the messenger RNA present in rhizomes across the developmental series, the researchers constructed a regulatory network and found a transcriptional hub composed of three families of transcription factors: NAC, ERF and bHLH. This NAC-ERF-bHLH module, active specifically in the root and rhizome tissue, appears to orchestrate the entire ring-forming process. It activates genes involved in phenylpropanoid and flavonoid biosynthesis as well as genes governing starch metabolism, thereby steering the plant’s carbon flux toward structural construction. In other words, a small set of master regulators coordinates the reallocation of sugars, the ramp-up of lignin synthesis and the mobilization of stored starch, all in service of building the segmented architecture.

The multi-omics integration also linked specific enzyme-coding genes to the visible anatomy. Genes encoding phenylpropanoid enzymes such as phenylalanine ammonia-lyase (PAL) and cinnamate 4-hydroxylase (C4H), the entry points of the lignin pathway, showed expression patterns strongly correlated with the timing of ring formation and the accumulation of lignin precursors. Genes encoding ABC transporters, membrane proteins that shuttle molecules across cell membranes, were likewise correlated with the anatomical and metabolic changes, suggesting a role in moving lignin precursors and other metabolites to the sites of wall deposition. This tight correlation between gene expression, metabolite abundance and tissue structure is what gives the study its persuasive power: three independent layers of evidence all point to the same underlying mechanism.

Why would a plant go to such elaborate lengths? The authors propose that the silkworm-like ring is the product of a carbon flow allocation strategy triggered by early autumn environmental signals. As days shorten and temperatures cool, these signals activate the plant’s phospholipid signaling system, which in turn switches on the NAC-ERF-bHLH transcriptional network. The redirected phenylpropanoid carbon flux leads to lignin precursor accumulation, which regulates both cork cambium activation and secondary xylem proliferation. The lignified rings that result improve the mechanical strength of the rhizome, allowing it to resist compression and maintain its shape in the soil. Meanwhile, the hollow cortex created by cell death may serve as an insulating layer that buffers the organ against heat stress, an adaptation that could matter in the exposed mountain habitats where N. incisum grows.

The compartmentalized structure may also serve the plant’s chemistry. N. incisum accumulates medicinal compounds in its rhizome, and the segmented architecture, with its alternating solid and hollow zones, could allow the plant to store these components in discrete compartments, separating them from the transport streams that move water and nutrients through the xylem. The study’s authors suggest that the combination of lignified rings and a buffered, hollow cortex together maintain organ stability while enabling this compartmentalized storage. If correct, the ring pattern is not merely an aesthetic curiosity but a functional adaptation that couples mechanical engineering with pharmaceutical chemistry in a single organ.

Beyond its evolutionary interest, the work has immediate practical value. Because the rings form during a narrow window in early autumn, growers now have a specific developmental target to aim for when managing cultivation. Understanding the environmental cues and signaling pathways that trigger ring formation could allow farmers to optimize planting schedules, soil conditions and harvest timing to produce rhizomes with the prized silkworm-like morphology. The identified NAC-ERF-bHLH hub and the key biosynthetic genes such as PAL and C4H also provide molecular markers that breeders could use to select lines with strong ring-forming capacity, accelerating the improvement of this rare and increasingly pressured medicinal species. All plant material in the study was cultivated at the team’s controlled experimental base in Tanchang County, Gansu Province, rather than collected from the wild, an approach consistent with conservation concerns for a species whose wild populations face harvesting pressure.

Scientifically, the study is a textbook example of what multi-omics integration can achieve in plant developmental biology. Neither the anatomy alone, nor the metabolite profiles, nor the gene expression data could have revealed the mechanism on their own; it is the convergence of all three that turns a morphological description into a causal model. The finding that a single transcriptional hub can coordinate carbon reallocation, secondary wall deposition and programmed cell death adds to a growing body of evidence that plant architecture is often governed by compact regulatory modules that respond to seasonal signals. For N. incisum, the message of the study is clear: the silkworm-like rings that have made this plant famous in apothecaries for centuries are the visible outcome of an autumn-triggered genetic program that trades energy for armor, hollowing the cortex and hardening the rings in a single coordinated sweep. The research, published open access in BMC Plant Biology, gives both scientists and cultivators a molecular handle on a trait that has been valued but never understood.

Subject of Research: Morphogenesis and molecular regulation of silkworm-like ring formation in Notopterygium incisum rhizomes

Article Title: Research on the morphogenesis of Notopterygium incisum rhizomes and its mechanism: multiomics integration analysis reveals the formation mechanism of silkworm-like rings

Article References: Zhao, W., Gao, J., Chen, H., Zhang, J., Lu, W., & Jin, L. (2026). Research on the morphogenesis of Notopterygium incisum rhizomes and its mechanism: multiomics integration analysis reveals the formation mechanism of silkworm-like rings. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09983-9

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09983-9

Keywords: Notopterygium incisum, rhizome, silkworm-like rings, plant morphogenesis, secondary growth, cork cambium, programmed cell death, lignin, phenylpropanoid pathway, multi-omics, transcription factors, medicinal plant