A study from Kobe University has uncovered how Balanophora plants, which do not photosynthesize and some of which reproduce asexually, manage to thrive as parasites on host plant roots. These elusive species, hidden underground most of their lives, offer new insights into plant evolution and metabolism. The findings highlight dramatic reductions in their plastid genomes while maintaining vital functions.
Balanophora plants represent an extreme in plant biology, abandoning photosynthesis to parasitize host roots for nutrients. They spend most of their lives underground, emerging only during flowering season in humid forest habitats. Some species have even forgone sexual reproduction, relying instead on asexual means to produce seeds.
Kenji Suetsugu, a botanist at Kobe University, led the research to connect evolutionary history, plastid changes, and ecological adaptations in these plants. "My long-standing aim is to rethink what it truly means to be a plant," Suetsugu stated. The team analyzed species relationships and found that all Balanophora members share a dramatically reduced plastid genome, a shift that likely happened in a common ancestor before diversification.
Despite the reduction, plastids remain essential. "It is exciting to see how far a plant can reduce its plastid genome, which at first glance looks as though the plastid is on the verge of disappearing," Suetsugu explained. "But looking more closely we found that many proteins are still transported to the plastid, showing that even though the plant has abandoned photosynthesis, the plastid is still a vital part of the plant's metabolism."
Asexual reproduction appears to have evolved multiple times, aiding colonization across islands from mainland Japan through Okinawa to Taiwan. "Over the past decade I have studied Balanophora pollination and seed dispersal where camel crickets and cockroaches play an unexpected role, but I also noticed that asexual seed production often ensured reproduction when mates or pollinators are scarce," Suetsugu noted.
The study, published in New Phytologist, was conducted with collaborators from the Okinawa Institute of Science and Technology and the University of Taipei. Funding came from the Japan Society for the Promotion of Science (grant 23K14256), the Human Frontier Science Program (grant RGEC29/2024), the Japan Science and Technology Agency (grants JPMJPR21D6, JPMJFR2339), and the National Science and Technology Council, Taiwan (grant 109-2311-B-845-001). Suetsugu plans further work to link these genomic insights with biochemical analysis of plastid functions in sustaining parasitic growth.