Ikoma, Japan—Parasitic plants are notorious agricultural pests that drain nutrients from crops and cause economic losses of more than USD 1 billion due to yield losses every year. Yet these plants almost never attack themselves or closely related plants. Scientists have long suspected that parasitic plants can recognize “kin,” but the molecular basis for this self-protection has remained unclear.

Now, a team of researchers at the Nara Institute of Science and Technology (NAIST) in Japan has uncovered the mechanism that allows parasitic plants to distinguish self from non-self. Their findings, published in the journal Science on October 23, 2025, point to new strategies for protecting crops from these parasitic plants.

The study was led by Professor Satoko Yoshida, who heads the Laboratory of Plant Symbiosis and included Professor Takayuki Tohge at NAIST, Dr. Ken Shirasu at the RIKEN Center for Sustainable Resource Science, and Professor Yuki Tobimatsu at Kyoto University.

“Parasitic plants, such as Striga and Orobanche, cause major crop losses. Understanding their self-recognition system offers a path to engineering crops that appear as kin and escape attack,” says Yoshida.

Parasitic plants invade their hosts using a specialized organ called the haustorium, which connects them to the host’s vascular system. The formation of this organ is triggered by chemical cues known as haustorium-inducing factors (HIFs), which are derived from lignin, a fundamental component of all plant cell walls. Because all plants, including parasites, produce these lignin-based signals, a key question arises: how do parasitic plants keep their own HIFs from triggering haustoria formation on their own roots?

To explore this, the researchers studied the parasitic plant Phtheirospermum japonicum. They searched for mutants unable to avoid self-parasitism and identified a mutant called spontaneous prehaustorium (spoh1), which formed prehaustoria on its own roots without any external signal, as if it could no longer recognize itself.

Genetic analysis revealed that this defect results from a mutation in a single gene, PjUGT72B1, which encodes a glucosyltransferase enzyme. When the researchers reintroduced a normal copy of the gene, the mutant plants stopped spontaneously forming prehaustoria. When PjUGT72B1 was removed, healthy plants began forming prehaustoria on their own roots, showing that the gene is essential for suppressing inappropriate haustorium development.

The team found that PjUGT72B1 acts as a molecular switch. It attaches a glucose molecule to the plant’s own HIFs inside its roots in a process called glucosylation. This modification neutralizes the signals and prevents them from activating haustorium formation. In the spoh1 mutant, which lacks this glucosyltransferase enzyme, active HIFs accumulate and leak out, causing the plant to form invasive structures on itself.

By revealing how parasitic plants suppress their own haustorium-inducing signals, this study opens a new avenue for crop protection. Strategies that alter HIF production or glucosylation could help develop crops that naturally repel parasitic weeds.

“Divergent substrate specificities of UGT72B1 between the parasite and the host enable discrimination of kin from potential hosts, suggesting a strategy to engineer crops that are effectively invisible to parasitic weeds,” says Yoshida.

IMAGE CREDIT: Satoko Yoshida from Nara Institute of Science and Technology, Japan.