Figure 1: A confocal microscopy image showing the initial stages of an haustorium developing in Phtheirospermum japonicum, as a model plant for parasitic Striga. © 2026 RIKEN Center for Sustainable Resource Science
Genes that play a key role in the formation of an infectious organ used by parasitic plants have been identified by plant scientists at RIKEN1. This discovery fills a gap in our understanding of how parasitic plants infect their hosts.
Striga and other parasitic plants are among the world's worst agricultural pests. In particular, Striga infections reduce the yields of rice, sorghum and maize across Africa and Asia.
Striga grow organs known as haustoria, which connect to the roots of their host plants and siphon away nutrients.
Max Fishman of the RIKEN Center for Sustainable Resource Science believes that haustoria could hold the key to controlling the parasite. "If we can better understand the biology of the haustorium, then we can start to plan ways to manage and control these parasitic plants," he says.
Striga is a parasite that needs a host in order to complete its lifecycle, making it difficult to study in the lab. Instead, researchers use another parasitic species, Phtheirospermum japonicum, as a model for Striga.
Fishman and his coworkers used RNA sequencing to identify genes that are active early in haustorium development in P. japonicum.
They knew that a crucial early step involved proteins being cleaved under specific conditions, so they looked for gene expression encoding proteins, which could be cleaved in those conditions.
The team found that a Root meristem Growth Factor (RGF) gene was activated. Further experiments confirmed that two other RGF genes were also upregulated when they induced haustorium formation.
Fishman and his coworkers found that treating plants with RGFs could induce the formation of pre-haustoria and activate expression of a gene involved in pre-haustorium development.
To determine which of the six receptors for RGFs are involved in the process, the team knocked each one of them out in turn. This revealed that two RGF receptors, RGFR1 and RGFR3, are required for haustorium formation.
Finally, the team analysed how RGFs had evolved a role in parasitism. They found that RGF5 was only found in P. japonicum and had recently evolved by duplication, suggesting that it has recently acquired a role in parasitism.
In contrast, RGF2 is shared between parasitic and non-parasitic plants. Consequently, finding out how it is regulated in different plants might shed light on how some plants evolved into parasites.
"That was really exciting for me," says Fishman. "It means that what we found isn't just specific to this plant. Ideally, we want our discoveries to relate back to important parasitic plants like Striga."
